Most of his development happened in the 60's because in the Ditko run he could be an utter ass and then he mellowed out in Romita, and then the book stayed being about following things that happened to him and his relationships with the personality of the Romita-era being the definitive one. There's not much to develop because he doesn't have many flaws anymore, like how there isn't much room for growth in ideal human Captain America, so at most you can try to tear him down and have him find his way back to how he was, which is just better for superheroes who's stories don't have known end-points. Spider-Man occasionally does a selfish thing but if he never did that in the name of character development and handling responsibilities better then he'd be more boring to read. I not too rarely do think he's boring to read (and that's mainly referring to older material.) It's a difficult situation on how to make a character so defined and popular "grow" without losing any more of his flavor.
Slott made Peter make ethical errors to show him as fallible like considering letting a girl die to get his body back for two seconds, or not admitting to plagiarizing a supervillain who screwed him over as it benefitted his own career, but this is also the same person who spent years manipulating the news industry and scrapping all journalistic integrity for profit, so. And even post-Slott he's still making big yet understandable boo-boos. And that's good. He can do some greasy things! The whole idea of the character was that good isn't his first instinct and he needs that extra lesson about responsibility to push him in the right direction.