Ok.
Just seemed to me that it could also be a deliberate choice to not have the 'player character' speak. Which has been a Nintendo staple forever, no matter how much other characters start getting voiced. FE 3H specifically, probably has more voice acting than any Nintendo game before. So, the Byleth character being silent, at least, doesn't seem to me to be directly a consequence of budget cutting.
Like the other game being discussed, Astral Chain. It has full voice acting for both characters, but the one you are controlling stays silent during the run of the game with that character. Play as the other character, and that one becomes silent while the other one talks. Budget cheapening, or deliberate design choice (whether you agree it is a good choice or bad choice)?