...before special late hours available for on-site guests was called E-Ride Night and there was a $12 charge. We were lucky to have this a couple years ago for one night and loved it!!! The late EMH hours is pretty much the same but FREE.
I can understand your frustration. One of the 'perks' for staying onsite was the exclusive use of a particular park on certain days, whether that was the extra hour in the morning, or the new EMH in the evening. With late hours until midnight, anyone in the Orlando vicinity can be visiting the parks, rather than just WDW guests. That will certainly mean increased attendance, which means longer lines.
However, there IS a difference between the old E-Ride Night and the new EMH perk. Under the E-Ride night, granted, we had to pay $12, but it was LIMITED to the number of guests who could take advantage of it. That helped tremendously in keeping the lines, attendance, etc. down in the park. With this new EMH system, the only limit is the number of people who are staying in the WDW resorts that day...which can be triple what used to be allowed in under the E-ride nights.
Unfortunately, it is a lesson learned from going during busy weeks, such as President's Day, Easter, etc. I myself am going during Grad Week, and have resigned myself to MK closing at 7:00 pm for both weekends.