Different characters and stories need a different tone, and it's what will keep them all fresh and interesting.
This is also what Zack Snyder really screwed up (and Whedon made even worse). Superman movies should not feel like Batman movies, which should not feel like a movie about The Flash or the Green Lantern. And if Snyder had understood that, then the team up movies would have been better as well, because characters' contrasting attitudes and values would have created opportunities for drama.