The irony of the film is that it’s central theme is about how, if you’re not careful, you can ruin the universe by creating too many alternate timelines.
By shoehorning characters from other universes and films, The Flash creates a convoluted mess that is exhausting to watch and ultimately less than the sum of its parts.
If this movie had taken it’s own advice and not created itself in the first place, our universe would be better for it (save for the Michael Keaton scenes).