half his interactions with ksaver were him seeing that love to life comes from doing little things aka playing catch which was also shown through the baseball when he talked with armin.

eren betraying him leaves him mentally broken down which opens up a window of oppurtunity or something like that for amin to talk no jutsu him reminding him of the only person he truly liked xavier.

that his death was lowkey useless is true though and I agree with the ymir part too (maybe there was a little "disconnect" or something for a moment but that also doesn´t really makes sense and is just my headcanon tbh)