Gunn's overwhelming praise for Flash definitely gives me pause.
I'm not a huge fan of his movies, as I don't really vibe with the undercurrent of ugliness or vulgarity he employs (Even in Guardians, I just find too much of it to be unpleasant. Taser Face and the fleshy planet are not really what I like to subject my eyes to).
Now I never expected him to bring that to Superman, but the fact that he apparently thinks a Flash movie with babies in microwaves, teeth falling out, an annoying character with spaghetti sauce and other food constantly being shoved down his throat, charred bodies, etc etc, and doesn't find any of that stuff to be out of place or cringy, so much so that he's bringing Muschieti back, definitely makes me think he might let that kinda stuff fly in his universe, in the wrong properties.
(Now, Brave and the Bold, given the Morisson comic's influence, might ironically be a property where that bizarro comedy/vulgarity might work, but still. It's alarming).