The stuff with Ace was character growth, the shit in the New World is same pig different lip stick. he does 2 things everytime, gets overemotional and rushes into things without thinking then punch punch punch, knocked down, then gets back up new powerup more punch punch punch
There is a difference with development and growth/progress.
Luffy from day 1 is someone who unconditionally believes in himself and goes after the dream he had as a kid.
The Ace stuff took that away, and his challenge was to overcome his loss and not lose his unconditional belief.
Like i said, not liking Luffy for what he is, i completely understand, and in the end matter of taste. Especially post-TS he has been too one-dimensional.
But Luffy was never the character that is supposed to grow, for better or worse, he is supposed to make his environment grow, at least mentally.