In my opinion, and as others already mentioned, it depends on the situation, ability, creative thinking and intelligence of the character.
First example: Luffy
He is strong, emotional and an idiot. But he can pull a lot of abilities out ofbhis devil fruit because he is creative with it. Sometimes the ideas are dumb, but it shows that Oda gives Luffy the strength to grow with his powers because he is capable of extending his usage in all kinds of ways. The emotional side though intercepts with his future sight for example, where you need to be clear headed and calm, which he rarely is.
Second example: Arlong
Arlong is a fishman, which are to be told 10 times stronger by natural strength than humans. And that shows. At the same time he is too comfortable in his position. His plan to conquer the islands of East Blue and expanding his territory went slowly over more than ten years because he felt he was the greatest but never faced any troubling enemies. And due to that he never grew stronger. He was overly confident with what nature gave him, but he didn't improve over the years.
Third example: Sugar
Her devil fruit ability is amazingly strong. Besides the side effect of not growing physically anymore, it feels like she never cared much about using the potential of her devil fruit. Instead she stayed hidden in her own small world down below Dressrosa and played with her toys. Being an underling of Doflamingo and being used to hide the dark secrets of their reign, she never had room to improve. What she was doing was enough for her. If someone used her abilities differently in different circumstances, she could be queen of Dressrosa, if not even queen of the whole world. But the plot made her unable to use that potential.
Fourth example: Katakuri
With his years of knowledge and strengthening his skills he is a very capable fighter. But he lacked opportunities to grow by fighting against people that were strong like him, which makes him lack the stamina to hold up against Luffy who continues to stand up and fight and who has always fought people stronger than him. Even if Big Mom used to travel around more with her crew, most of them nowadays reside in Totland sitting on their lazy asses because rarely ever someone strong who made it that far in the new world will try to invade her territory and cause a scene.
In conclusion: Depending on the circumstances, depending on the position the people are in, depending who or what they are working for or towards, the characters only have certain strengths and abilities. I don't think Oda sucks at it, but if you look at why the characters are as they are you come to see that there are the reasons for their "power level".
On another hand, there's the "inconsistency" of beating someone but being beat easily by someone else.
Example one: Luffy against Katakuri and Kaido
Luffy fought against Katakuri (bounty of ~1 billion) for more than ten hours, and faced extreme difficulties fighting against him?That makes sense. Luffy barely scratching on Kaidos (4.6 billion bounty) surface and being one-shot by him? That makes sense as well. Kaido is the strongest creature alive, has an awfully high bounty to show his strength and threat level. He fell down 10.000m and got away with a headache. Kaido is a yonko and not a joke. Just like Big Mom tanked Gear 4 without issues or an extreme lightning strike by Nami. They have incredible endurance. Luffy though now trained to become stronger and didn't sit on his lazy ass drinking unlike Kaido. He is better prepared and has people who may assist him in the fight.
Example two: Zoro against Kamazo (Killer)
Being adressed is "Zoro fainting from one stab wound". This is just my view as I see it and people can see it differently if they want to. Zoro chose to protect a woman and a child while facing Killer and Gyukimaru. While Zoro and Killer engaged in fighting, Gyukimaru used the opportunity to butt into the fight, causing Zoro to be stabbed by Killer. He additionally flexed his muscles while Killer tried to pull out the weapon but was unsuccessful. This could have made the wound tear further. Zoro then used the gained weapon to defeat his opponent. The wound, being a stab wound piercing through his whole shoulder resolved in massive blood loss. It is one serious wound instead of just being beaten around for a while. And by seeing that, Gyukimaru chose to leave instead of fighting someone "who received a stab wound and looks like he's gonna die from it" by logical thinking. So Zoro considered the threat to be gone and gave in to his wound and became unconscious. He had those issues a lot already. Be it Buggy stabbing him, and Zoro escaping with the cage but then going to sleep afterwards or Zoro fighting against Mihawk, where he as well didn't last long after receiving a stab wound.
In conclusion: In my opinion power scaling is being handled well by Oda, the true problem lies in the incapability to read or analyse by some fans/readers and trash talking characters due to incomplete knowledge or basing their statements on assumptions made out of nowhere.
First example: Luffy
He is strong, emotional and an idiot. But he can pull a lot of abilities out ofbhis devil fruit because he is creative with it. Sometimes the ideas are dumb, but it shows that Oda gives Luffy the strength to grow with his powers because he is capable of extending his usage in all kinds of ways. The emotional side though intercepts with his future sight for example, where you need to be clear headed and calm, which he rarely is.
Second example: Arlong
Arlong is a fishman, which are to be told 10 times stronger by natural strength than humans. And that shows. At the same time he is too comfortable in his position. His plan to conquer the islands of East Blue and expanding his territory went slowly over more than ten years because he felt he was the greatest but never faced any troubling enemies. And due to that he never grew stronger. He was overly confident with what nature gave him, but he didn't improve over the years.
Third example: Sugar
Her devil fruit ability is amazingly strong. Besides the side effect of not growing physically anymore, it feels like she never cared much about using the potential of her devil fruit. Instead she stayed hidden in her own small world down below Dressrosa and played with her toys. Being an underling of Doflamingo and being used to hide the dark secrets of their reign, she never had room to improve. What she was doing was enough for her. If someone used her abilities differently in different circumstances, she could be queen of Dressrosa, if not even queen of the whole world. But the plot made her unable to use that potential.
Fourth example: Katakuri
With his years of knowledge and strengthening his skills he is a very capable fighter. But he lacked opportunities to grow by fighting against people that were strong like him, which makes him lack the stamina to hold up against Luffy who continues to stand up and fight and who has always fought people stronger than him. Even if Big Mom used to travel around more with her crew, most of them nowadays reside in Totland sitting on their lazy asses because rarely ever someone strong who made it that far in the new world will try to invade her territory and cause a scene.
In conclusion: Depending on the circumstances, depending on the position the people are in, depending who or what they are working for or towards, the characters only have certain strengths and abilities. I don't think Oda sucks at it, but if you look at why the characters are as they are you come to see that there are the reasons for their "power level".
On another hand, there's the "inconsistency" of beating someone but being beat easily by someone else.
Example one: Luffy against Katakuri and Kaido
Luffy fought against Katakuri (bounty of ~1 billion) for more than ten hours, and faced extreme difficulties fighting against him?That makes sense. Luffy barely scratching on Kaidos (4.6 billion bounty) surface and being one-shot by him? That makes sense as well. Kaido is the strongest creature alive, has an awfully high bounty to show his strength and threat level. He fell down 10.000m and got away with a headache. Kaido is a yonko and not a joke. Just like Big Mom tanked Gear 4 without issues or an extreme lightning strike by Nami. They have incredible endurance. Luffy though now trained to become stronger and didn't sit on his lazy ass drinking unlike Kaido. He is better prepared and has people who may assist him in the fight.
Example two: Zoro against Kamazo (Killer)
Being adressed is "Zoro fainting from one stab wound". This is just my view as I see it and people can see it differently if they want to. Zoro chose to protect a woman and a child while facing Killer and Gyukimaru. While Zoro and Killer engaged in fighting, Gyukimaru used the opportunity to butt into the fight, causing Zoro to be stabbed by Killer. He additionally flexed his muscles while Killer tried to pull out the weapon but was unsuccessful. This could have made the wound tear further. Zoro then used the gained weapon to defeat his opponent. The wound, being a stab wound piercing through his whole shoulder resolved in massive blood loss. It is one serious wound instead of just being beaten around for a while. And by seeing that, Gyukimaru chose to leave instead of fighting someone "who received a stab wound and looks like he's gonna die from it" by logical thinking. So Zoro considered the threat to be gone and gave in to his wound and became unconscious. He had those issues a lot already. Be it Buggy stabbing him, and Zoro escaping with the cage but then going to sleep afterwards or Zoro fighting against Mihawk, where he as well didn't last long after receiving a stab wound.
In conclusion: In my opinion power scaling is being handled well by Oda, the true problem lies in the incapability to read or analyse by some fans/readers and trash talking characters due to incomplete knowledge or basing their statements on assumptions made out of nowhere.
