Frostbite or Dawn Engine with its bad editors and performance problems?
Crytek used by few games? (This one has a chance to challenge UE) Unigine which is also rather rare?
For example if I wanted to make a 3D platformer in unity, I could probably commission an artist to create the character, download a starter kit of some sort, and be done with it in about a week.
However this means I'm tying in so much code, and if anything doesn't work exactly the way I expect it I can complain. I might complain about the starter kit I purchased, I might complain about Unity crashing when the real reason for the crashes are my own crappy code.
Particularly when I was younger, I would often try to do way too much at once and this leads to frustration. But, theoretically you could create the next gears of war with three other people in about a year. Odds are you're going to run into tons of problems though just because it's so hard to do that
this is simply not true