I'm trying to think of how one would test this via looking at data and it's difficult as Orlando has not added a large amount of capacity since adding AK. Of course crowds have gone way up since then but they probably would have gone up either way.
I do think that Disney could do more to add capacity instead of refurbishing / replacing old rides. That said, I also think there is at least some element of exclusivity at play - people want to ride hard-to-get rides in part because they are hard to get. Even "pretty good" rides like Nemo and Little Mermaid generally have low wait times. So it's also possible that if there were ten new big ticket attractions, only two of them would be hot tickets and the rest would be the new equivalent of Nemo, just because people go after the thing they can't have (or that's hard to get). So while I think new rides are important to keep the parks interesting and relevant, my thought on reducing crowds is that other forms of people-eaters are needed.