There has DEFINITELY been a line every time I've gone. Even at the slowest day. On a very slow day (where the Hulk and Spiderman are walkons), the Harry Potter park was a walk in, but there was a 35 min wait for the WWOHP ride, and a 45 min wait for the wand shop. I also had to wait in a line that started behind the bar in Hogsmeade just to get a butterbeer, don't remember the wait but it was longer than anyone should have to wait for any drink at that bar. I only went this route because the various butterbeer carts all had MUCH longer lines.
Do I go every day? No. Are there some days that are probably slower? Sure! But either way, this tells me this place needs to expand just to spread out the crowds. Even on that slow day with probably a third of the people you would normally see there on a crazy busy one, it was STILL a beast to navigate through people. Could this be poor design? Poor Flow?
Not really too much of a fan of the HP franchise, but I really do like that part of the park. That being said , we avoid the hell out of it because the congestion sucks. We'll sneak in the JP side, ride WWOHP, say "we've rode dueling dragons millions of times, we'll skip it," then talk the kids into doing something else.
This place definitely NEEDS to expand.