Everyone says the enderdragon is hard. I think momentus is hard I spent 15 minutes fighting the enderdragon on single player mode but an hour and a half seriously momentus I personally think should not be able to teleport you but hey then gain it makes it a challenge
It also makes a difference that Ender Dragon is vanilla, and Momentus is only on EMC. And Ender Dragon's don't spawn on EMC.
I think the difference lays in the massive damage a momentus does, an enderdragon just flies around damaging you every 2 hours or so...
The Ender Dragon is really weak and the only thing that keeps it alive is its crystals and its flight speed.