Removing a character as obligatory as Peach is grounds for a “0/10” on its own. From that point forward every single new addition will be held under heavy scrutiny for being deemed a higher priority than the most important female Nintendo character. It casts a shadow on the entire roster, I think that's what some people have to consider when making arbitrary character trades that simply trail behind in inherent value.
Smash already doesn't really operate in terms of "replacement", although that is susceptible to change moving forward if roster space is particularly limited. But certain characters like Peach, Meta Knight or Isabelle do not have equivalent exchanges. They are too important to their series and far too popular to feel justified swapping out for another "rep" within their series. In what world Resetti outprioritizes Isabelle, or Dark Matter over Meta Knight, I'm not sure. God forbid Peach, one of the most unique characters on the roster and one of Nintendo's most popular characters, is swapped out for Captain Toad.
This is admittedly the most difficult balance when plotting out smaller rosters. You want to do something new, but there are certain choices that can't really be walked back on by a simple newcomer band-aid. New for newness sake is not Smash's forte and it creates rosters that feel built around shock value more than any coherent ideals.