Even that is dependent on how many people actually show up. If there are 10,000 people at the Magic Kingdom for early entry (I don't think there will be, but who knows) and you're one of the last thousand in 15 minutes later than everyone else there could easily be 30+ minute waits for some (if not all) of the major attractions. That's still a shorter wait than you'd have otherwise, but it's not really a big enough perk to justify the hotel prices.
It could be even more of an issue at the other parks where everyone would head to a smaller number of attractions and thus concentrate the crowds/wait times, although they will likely all have less people showing up than the Magic Kingdom which helps ameliorate that problem.
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.