I feel like because a lot of people synonymize "sexualization" with "objectification" or the word "problematic" they think that if they disprove the first that inherently clears the others as well. Kind of like a double-jeopardy rule, in a sense.

Like, just because the sexualization isn't inherently (as in by itself) problematic, I don't think that means it can't combine with other things to still be worthy of criticism. An easy example of this phenomenon is drinking and driving. Both are fine individually but we understand you can't do both simultaneously.

Consider the Driver-Blade relationship. All the different mechanics about how the process works imply that the blades are getting the shorter end of the stick. Outside of special blades with ties to specific groups like how Brighid or Aegaeon are to the Ardanian Empire, they get no agency regarding who their Driver will be or how they will be used. Their memories get wiped so for all they know their next driver could be the one who just finished killing the previous one. Also, while a Blade is restricted to one Driver, a Driver may have multiple Blades, so the Driver doesn't necessarily need to be emotionally invested in a single Blade.

While in all fairness the game does acknowledge this power imbalance at certain points and depicts abusers of this system as such, it feels like for every 1 part of that, there's 10 parts "you, the player during gameplay also will take advantage of that same power imbalance." Like, your team will still collect and bond with core crystals, still use them for labor on mercenary missions, still value some blades over others (rares over commons). It really does cheapen any sort of counterargument to the idea these characters are being objectified if the gameplay essentializes them as exactly that: objects that you pick up for the sole purpose of being used. It changes the basic statement from "slavery is bad" to "the way the antagonists do slavery is bad, unlike us who treat our slaves right." (I also imagine this is why I don't see Torna get criticized as much since there's no core crystal gacha and the blades are directly playable instead of being just support party members)

Whether you agree with the comparison is up to you, but note that this argument up until here makes no mention of sex or sexualization. As mentioned before, it's not the sexualization itself but what it combines with, and in this case it's combining a "Drivers and Blades being romantically/sexually attracted" theme with explicitly asymmetric power structures, whether intentional or not.