I mean there is enough fun lack of realism and fantastical elements in both the GTA and Red Dead series to not be like adding a straight-up normal dude into Smash. The supernatural (Big foot, ghosts, aliens, clones, the beast, the devil, zombies, a vampire, a time traveler, etc), special abilities (Red Mist, Bullet Time, Driving Focus, Dead-Eye), super high tech (Jetpack, Deluxo, Oppressor, Up-and-Atomizer, etc), and plain bizarre (Carrying multiple weapons, being a one-man army, the epsilon program, real fortune tellers, nutjobs, etc) are part of the satirical worlds we see in GTA and Red Dead games even if it isn't as apparent as in MGS. Even then, in Smash, Snake is just a normal-looking dude with weapons anyway so it doesn't really matter.
Though with them being more realistic and down-to-earth like Snake, I also want them specifically as they don't fit in with the "animes" and "cereal mascots", there are very few characters that skew away from that like Snake and Samus. They can be more unique and interesting as a result of their juxtaposition. I like the idea of having more standout characters and variety instead of a fighter blending into the sea of characters. Smash is a celebration of Nintendo and gaming according to Sakurai, but it feels like a certain style isn't getting a proportional enough amount of love as the other games. (At least in the character select screen.)
This is Smash after all, so I like the mishmash. It isn't like Mario Odyssey where New Donk just has realistic-looking humans for no reason despite Mario having such a neat art style normally. Though I've slowly warmed up to the humans and it isn't as weird in the New Donk Stage.