It's a real take. You can't look at RS and Exoskeleton shit and say: "That's some progression, love Sanji and his hard work".
Mind you all of that after he wanted nothing to do with the Germas anymore cause it's a painful time of his life for him.
But the hard work is there
Zoro wouldn't achieve the things he did without Enma, his merit is at saving Hyiori, giving away Shusui and taking Enma with him, its at letting Enma have a chance to suck him dry, pushing him to his limit, using the Mink Elixir to fight again, put his life on the line and so on...
Luffy wouldn't have did the things he did without haki training and his Devil Fruit, but he needed both anyway, the merit is at training, at fighting stronger foes than himself, and at consequently awakening his DF.
Sanji wouldn't have achieved the things he did without the Raid Suit initially, which leads to the Exoskeleton awakening, that is basically an stat booster. Sanji's merit in this lies on his whole character and the decisions he made all along, especially with the events of WCI. To be more specific with the Wano arc, his merit is at using the Raid Suit because "someone could die if he didn't throw away his pride" and that being a literal thing later on, is at refusing to beat his actual enemy using the suit while being crushed to death, is at destroying the suit even it means defeat.
Not everyone can wield Enma. Not everyone can awaken Luffy's Devil Fruit by basically dying, not everyone can make the choices Sanji made. Not everyone can use CoC coating by giving a sword the chance to kill you. Not everyone can be so proficient with the 3 types of haki like Luffy does. Not everyone can put his bones back on their places after being crushed by something that supposed to kill "Armament Haki masters", not everyone should be able to literally go invisible permanently solely by being fast, much less using flames that can arguably outmatch all the Fire based Devil Fruits powers.
The deal with that is: They are only doing this, because no one else could come close, and even if someone else did, they would hardly be able to do the same things strengthwise
The truth is that they need to evolve faster and hype their enemies as strong opponents at the same time, and thats why Oda did all this, they need to develop incredibly faster strengthwise to be able to reach the top in their 20s.