Smash4 was unimpressive, but Brawl's builder… you could spend hours making some really epic stuff and set any soundtrack you want to it. An unfortunate loss

I think this might be because of the Inling's inclusion.

Think about it, they had to code a way for every bit of every floor in this game to be inked based on its shape. It the stage builder was added and included all these other kinda of shapes like Smash 4's dud, imagine how difficult it would be for the ink to react to such an unpredictable stage.