Exactly. If they'd announced this before launch, it would've been the only thing anyone talked about. There would have been a huge backlash and I'm sure a good percentage of the community would've dumped the series there and then.
If they place something behind MTs, then I completely agree. But, if they want to add more cosmetics that don't exist yet, and they finance it MTs, and at a fair price, it's less unethical.
Announcing it after reviews... Hm. Sketchy at best.
If you tried the customisation, it feels extremely bare bones in comparison to Tekken 7. So I wouldn't be surprised if stuff was removed to add to the Store.
Adding shit to a game with a patch, post purchase, doesn't require you to partake. While I hate MTX as much as anyone, you aren't required to buy anything. Sure, this is enshittification, but you can avoid that buy buying games that aren't "always online".