There weren't 10,000 people at MK for EMH... and now early entry is at all 4 parks, as opposed to just one park, which will more evenly distribute on-site guests.
Of course, it will depend on the time of the year and the time of the opening. Animal Kingdom 7:30 a.m. early entry in May, I wouldn't expect a huge crowd gathering. Yes, if you're in the back of the early entry line, you may have a 20-30 minute wait for FOP, but that's still a decent advantage.
But 8:30am early entry at Magic Kingdom during Christmas week, would be a mad house.
Here is the thing to remember about the "perk" -- While it may not seem like a huge win for on-site guests, it really is very very punitive for off-site guests. Off-site guests completely and totally lose the ability to rope drop any park.
As things stood under EMH -- Typically, no more than 1 park would have EMH morning. So off-site guests could rope drop the other 3 parks, the same as an on-site guest. So if they got there early enough, they could ride Mine Train or FOP without any real wait.
But now, rope drop is on-site guests only -- Even if it was only a 10-minute advantage, that's still huge. That's the difference between doing FOP, Slinky Dog, Mine Train -- with a minimal wait, versus doing it with a 60+ minute wait.
So early entry may not seem like a huge win for on-site -- until you compare it to off-site.