RDJ isn't perfect Tony Stark.
Stop calling him "the perfect fit for Tony Stark", because he's not. Downey Jr. is very different from the comic book Tony Stark almost in every way. RDJ's Stark is self-obsessed, eccentric, narcissistic, douchey. Comic book Tony Stark is self-critical, serious, dark, empathetic, and more likable. Comic book Tony Stark never would call little kid a pussy for no reason.
To give you a context:
Comic book Stark.
https://pp.vk.me/c630919/v630919187/e97f/mJehvc9sFZU.jpg
Movie Stark.
https://66.media.tumblr.com/2a4d39d82ab60eb3f1fc65c01bd7ce0c/tumblr_inline_mza61vFAdV1rl9545.gif