From my experience, they have steadily increased. A level 6 is way more crowded than what a level 6 in 2010 was. Disney has come up with discounts, packages, free dining and other perks to fill the parks, especially during what used to be traditionally slow times. It's all in what you're looking for, and how you choose to tour. IMO, gone are the days when you could stroll into the park at 9-ish, 10 am and walk up to rides or pull passes and go see other attractions while you wait for your fast pass time. You don't just go for a couple of hours and do a few things, go back to the room to chill, then go back in the evening to do all the things you hadn't done while parades or fireworks are going off. Walking up to a sit down restaurant and getting seated within a couple of minutes is a thing of the past as well (unless you're very fortunate), Everything needs to be planned now and if your touring style is a relaxed, play it as you go style, you will probably be disappointed and frustrated as I have been the last couple of trips. For me, it's a whole new learning process and it's sort of bittersweet because "YAY" I'm getting the hang of it, but "BOO" that's not my style. I think if I didn't have 2 little grandchildren, then WDW would, for me, be a thing of the past. However, I put my personal experiences aside and as long as they are happy and are enjoying themselves, then I'm fine. So, for now, I'll rope drop, pre park ADR, fill a schedule with fps, ADRs and plan our every step but reluctantly. This time, though, we're doing early (really not my style), working in down time (resort and pool - a must for my sanity) and later evenings while skipping crowd attracting events in order to catch a few more attractions.
ETA: Correction - walking up to a restaurant OF CHOICE and getting seated...