While they aren't at capacity every day, they often hit capacity on weekends throughout the year. The parks have huge walkways and tons of attractions so they hold the huge crowds far better than DL, which was never built with today's crowds in mind
What's amazing about TDR is that it's the only resort where the second gate did what it was supposed to do - TDS is hugely popular and is equally crowded as TDL. That's what happens when the second gate is built correctly from the start, which didn't happen in Anaheim or Paris.