I know I'm late to the game on the DME conversation but it's worth pointing out that this is a one-size fits all program.
Disney is planning for folks who are (a) potentially not familiar with MCO, (b) may need to check luggage, (c) likely do not have pre-check, and lastly (d) allow time for potential delays with traffic, security or other unforeseen issues. So Disney operates in that 3-4 hour window as they see fit to ensure that nobody misses their flight because the worst way to end your Disney vacation would be to miss your flight and it is the Mouse's fault.
Now, I've heard people say, why doesn't Disney allow you to pick your window (sort of like "super shuttle" does). Well...if you've been to Disney recently you certainly realize that there are some "interesting" folks wandering around. People would not have the understanding or common sense to realize that they need more time. Everybody would choose "more time at Disney" resulting in panic and potential missed flights once they realize they've cut it too close.
If somebody in the know wants to game the system and "cut it closer", they could probably just tell DME a flight time about an hour after their actual flight and make that work. (I don't know that this works or not, just suggesting it).
For us, I've always felt that the arrival time at DME allows for a stress-free final few hours in Orlando. We arrive with plenty of time, find a quiet bathroom on the lower level to change. Make one last gift shop stop before heading through security and enjoying a leisurely dose of Jersey Mike's with just enough time to use the bathroom before board. I've never found us needing to "waste" more than 15-20 minutes.