William

He was there since Winter Soldier, the 2ND Captain America movie which takes place after The Avengers. Sam was not an OG Avenger by any means. Arguably he didn't even become one until after Civil War.

I'm sorry but you lost me at "detailed character development." There's barely any to speak of. It's like saying Dragon Ball has amazing character development. Don't get me wrong I enjoy both equally but saying it has great development is a bit of a stretch.