I'm not quite sure time has necessarily anything to do with it so much as being allowed to tell a good story without inference. You've hired good filmmakers, now let them do their job and tell their story.
For example, Sam Raimi made Spider-Man 2 only two years after the first Spider-Man and he was allowed to make the film he wanted to make. Spider-Man 3 was released three years after the second film but had a lot of studio and producer inference which led to a compromised quality.
While Favreau did voice concerns that he would be unable to make Iron Man 2 in the timetable that Marvel wanted, I think had he been allowed to make the film uninhibited he could have made a better film. Then again, that was probably only one factor in many that contributed to the lackluster quality of Iron Man 2.
The Venom storyline was one of the best bits of Spider-Man 3 and I can't blame the studio for forcing Venom into the movie. Raimi wanted to focus on Sandman, a character so one-dimensional that Raimi had to give him a bunch of cliches (sick kid, the whole I'm not an evil man crap) in a failed attempt to make him interesting. When that failed, he decided to take a piss on the origin story of Spider-Man, an even worse crime and one that doesn't help the first film if you chose not to ignore the third one.
Seriously, Raimi can take his "complex", not evil villains and cram them.
I can imagine the problems with Marvel didn't help but Favareu did himself no favors by presenting little action in Iron Man 2. He gave us two uncompelling villains. After the impressive racetrack scene, Mickey Rourke's character does nothing but lurk in the background and mumble until he returns in one of the most unimpressive fights of all-time. Sam Rockwell's character was an annoying, bumbling fool who was there only to make Tony Stark's character look good. As the very end, he wasn't even a threat to Pepper Freakin Potts! Some villains they turned out to be.
Add to that instead of doing Demon in a Bottle, Favareau decides to waste time on the "Tony is dying" storyline when we know damn well that isn't going to happen. Marvel might not of helped but the director could have done a lot better job.