I have been to both MK and Epcot on their busiest days both pre-park reservations and post park reservations
There are no comparisons.
The cap they've put on the parks with regards to reservations keeps the parks from reach the capacity they used to reach pre-park reservations.
That's when they hit the busiest days you can imagine with bodies crammed in to ever nook and cranny. Even then, parks never truly hit that "no more guests admitted period" level. They hit the "no more walk up, single ticket sale guests" level for brief periods but that's about it. AP, On Site guests, Guests with ADR, etc still got in.
The parks now, with their reservation caps, never reach those levels. Guess they never will again, unless we see the reservation system die.
Last year at NYE, when I'd see the worse lines ever in the past, I found no lines. I was shocked. All reservations were gone, so parks were at the max but the number of guests were probably at half what I'd see in the past. In some ways, it was not as fun either. I didn't miss the lines mind you but those crowds are what made the atmosphere at NYE at Epcot. The party was diminished