I shared this reaction at first too. It seemed like each MK for a while did a different and more intricate take on each character, and each of these redesigns are so much more grounded in a way that feels less fantastical. I couldn't help but dislike the fact that everyone just sorta...looks like a person.
I think I've come around to the idea though. I had this weird feeling as MK12 got announced and we were waiting to see stuff where I was excited, but kinda felt like we just did this with MK11. Like "okay, I guess maybe we'll see Reptile this time, maybe we'll get Ermac, would be cool to see what they do with Nitara" but at the end of the day we were just kicking the tires on the same old characters with a few glow-ups here and there, adding a mechanic or two, upping the stakes on how nuts everything is in the story and world to the point that the grandiosity and outlandishness gap between games starts closing. To kinda bring everything back down to earth with a less immediately intense aesthetic, and more understated designs, it feels refreshing to me.
All that being said though, I do hope we get some more cosmetic options too. I'm fine with the canonical looks for this game being less gaudy than in previous games, but I like a wacky costume as much as the next person.