I'm not sure how much busier they actually will be. Sure, lots more people on-site, but what they are mostly doing is getting people to switch from staying at Disney or some off-site hotel on I-Drive. Sure attendance will go up, but I wouldn't say "a lot" more crowded.Parks are going to be getting a lot more crowded when these rooms come online.
Besides, by the time these hotels open, Volcano Bay will likely have already expanded and Super Nintendo World will be right around the corner. It's those additions that will drive attendance, not the hotels themselves - hotels are just a place to stay, Universal is just making sure that people are staying with them now.