Huh. I'd ask why IW had to be a fun-filled commercial for the next MCU, instead of the gritty, ominous, gut-wrenching film I was expecting. Feige must be doing something right tho, and people like me who think it'd be a lot more interesting to see Tony Stark, Antman, etc. come up with a way to turn things around (as opposed to bringing in Mary Sue to save the day) can just go cry in a corner and re-watch TWS.
Based on Dr. Strange's actions in IW we already know that Tony's presence is a key. That probably wouldn't be the case if all he did was sit on the sidelines and eat popcorn while Captain Marvel did all the heavy lifting. Given that it's an Avengers movie, I'm expecting a collaborative effort, with both Ant-Man (quantum realm) and CM bringing new assets to the party.