I think the biggest problem with the Metroidvania genre (and other "(game)-like" genres in general) is that it creates games that are entirely derivative by nature.
Now, I don't think that taking inspiration from other games is inherently a bad thing, however the vast majority of Metroidvania games tend to be comfortable retreading the same grounds as Metroid and the IGAvania games, without much in the way of innovation or developing the genre further.
Personally, I think that Metroidvanias should be called platform-adventure games. It's a bit of an older term that I recently discovered, and I like it because it isn't too clunky (unlike search-action), reflects on existing game genres (platformer and action-adventure), and includes a broader scope of games.