Right, because that's a deal Sony would offer. "Here's Spider-Man for all your team up MCU movies, but don't worry, we're not going to use any of your characters for our solo movie."
Who says that he's going to defeat Spider-Man's villain? The guy has JUST been cast in the movie and already it's an Iron Man movie now? Cause that's what you're implying if he's going to defeat the villain with or for Spidey. We don't know the context of his appearances in or out of suit. Maybe it's something Peter can't handle so he calls in for assistance? Oh wait, that would be terrible considering it brings down Peter Parker's ability to be a "lone wolf".
Let me stop you RIGHT there where you start spitting out nonsense about not needing Iron Man to sell tickets.
MCU box office average with RDJ: 1.07B
MCU box office average without RDJ: 533M
The numbers are a bit skewed because of the Avengers movies, but they are what they are. Oh and by the way that number is going to climb after Civil War makes over 1.07B, just saying.
It's pretty naive to say that Spider-Man is good on his own because of 10 minutes in Civil War. It takes more than just that for him to have a successful box office draw (assuming the movie is good). I'd say without RDJ the movie would do Winter Soldier/GOTG numbers, slightly higher. In the 800M range, maybe SM3 numbers with good WOM and a decent RT score. With RDJ this becomes a billion dollar movie, period. That's why he's in it, and I can't wait!