It is actually pretty clever to add a time limit to some of Luffy's Gear-stages. Take for example Dragon Ball: Akira Toriyama had to come up with more and more ways for Son Goku to always become stronger and show how much he did so by inventing more stages of transformations. We had Super, Ultra, etc.. With a manga, that focusses mostly on fights, Dragon Ball mostly served the readers, who wanted to see interesting fights - and we got those!
With One Piece however, it is different: Oda is not solely focussing on interesting fights. I remember that once Oda told in an interview that he has gotten tired of drawing fights. His tiredness may however not be the reason for this time limit. But with this statement, we can see, that he does not focus on the fights in his manga this much, but on the plot. Actually, he sometimes sacrafices fights for the plot, as seen with Kizaru vs. Luffy (They will clash later with Kizaru not even shown, what he can do, yet.). And this priority comes also shining through with Luffy's fighting abilities. Oda tries to always add something to Luffy's inventory - an ability more. And with every arc, we see him gain more and more powers. But, he does this very slowly and carefully as to not exhaust Luffy's possibilities to get better. This way, he can add more wothout having to invent another stage or "Gear" just yet.
With Dragon Ball and the ending of the Boo-saga, I sometimes had the feeling that the Super Saiyan 3 was only added to give Son Goku that one transformation to top everyone. It felt odd to be honest. And I think Oda does not want it to be felt this way. So, to not always have to invent new Gear-stages, he slows the progression with how fast Luffy can master them and adds therefore a time limit to some. This way he also can also add more tension to fights and arcs (seen in Dressrosa). And this felles more harminizing with the plot, in my opinion. But I am also not the person, who reads the manga because of the fights, if I my be honest here. I am rather a fan, who likes good plot rather than a good fight. 😊 Therefore, a time limit does not bother me as much as it does you, maybe... .
With One Piece however, it is different: Oda is not solely focussing on interesting fights. I remember that once Oda told in an interview that he has gotten tired of drawing fights. His tiredness may however not be the reason for this time limit. But with this statement, we can see, that he does not focus on the fights in his manga this much, but on the plot. Actually, he sometimes sacrafices fights for the plot, as seen with Kizaru vs. Luffy (They will clash later with Kizaru not even shown, what he can do, yet.). And this priority comes also shining through with Luffy's fighting abilities. Oda tries to always add something to Luffy's inventory - an ability more. And with every arc, we see him gain more and more powers. But, he does this very slowly and carefully as to not exhaust Luffy's possibilities to get better. This way, he can add more wothout having to invent another stage or "Gear" just yet.
With Dragon Ball and the ending of the Boo-saga, I sometimes had the feeling that the Super Saiyan 3 was only added to give Son Goku that one transformation to top everyone. It felt odd to be honest. And I think Oda does not want it to be felt this way. So, to not always have to invent new Gear-stages, he slows the progression with how fast Luffy can master them and adds therefore a time limit to some. This way he also can also add more tension to fights and arcs (seen in Dressrosa). And this felles more harminizing with the plot, in my opinion. But I am also not the person, who reads the manga because of the fights, if I my be honest here. I am rather a fan, who likes good plot rather than a good fight. 😊 Therefore, a time limit does not bother me as much as it does you, maybe... .
In a one vs one Kizaru wins