If I ever create an RPG, it would be a good idea to put an invisible timer on the main quest, and if you don't complete it... nothing visible happens, but by the time you reach the final boss, he had completed his evil quest, your wifu dies, your home is burned to ground and you get the hardest battle of your life.
On the other hand, if you do only a reasonable ammount of side quests, then you battle him before he completed his goal, and you can actually get the good ending.
@apropos @Jens_Rasmussen
Yeah, that's the sad part, that if I were to do it, it would literally be the first thing everyone would hear about the game, making the mechanic meaningless.
It actually reminds me of a quest in Pathfinder Kingmaker, where an opposing barbarian is going to enact a ritual and you have to go stop him.
If you are too slow to go there, then he completes the ritual and the boss fight against him becomes harder and the quest's ending is not as good. Not really something that determines how things go at the end of the game though.