When was the last time you were in a WDW water park? Crowd tolerance certainly varies from person to person, but we've been to the water parks at least 40 times over the past 15 years, and I can't ever say I've had any of the issues you mentioned. Even 4th of July week, we never have a problem finding somewhere to sit. It may not be exactly where we want, but we always find plenty of spots. The only time we have to "push" through lines is in spots where several rides share the same sidewalk as the start of their queue. During peak hours, that can get crowded. But the rest of the parks aren't that bad.
For me, it would get too crowded if every slide has a really long wait, the wave pool is unreasonably crowded AND the lazy river is too...but never had that happen yet.