OK, maybe I shouldn't say going in that direction was "mistake", it is just not the direction I want to see these characters go in.
I don't think there is any way I could possibly, ever disagree more with what you just said about the MCU. The humor absolutely in no way deflated the situation, it was the best possible thing they could do in the situations they were in because it kept thing light and fun, didn't let them get to dark.
The MCU, and the Arrowverse are exactly what I want from my superheroes.
There are some things, like the Last of Us and The 100, where I expect things to be dark and grim, but that is not what I want from characters like Superman. I go to movies like that to get away from that kind of stuff.
Hell, even The Last of Us, and The 100, as grim and dark as they still find moments of lightness, fun, and positivity.