As much as Disney controls their own properties i don't think they have any say so on the original characters other then approving interactions with their characters. Master Xehanort turn to a sympathetic villain is just the work of Nomura.
Nothing MX says in KH3 matches his actions of BBS. It's like no one can be a straight up villain anymore after Thanos.
It also makes Kairi useage even more dumb. Master Xehanort plan is to kill Kairi to force Sora to fight him. But he was gonna fight him anyway. Its like
"MX-I need to force u to fight me
Sora-No u dont. Im gonna fight u anyway
MX-But i need to make sure. I always plan for every obstacle
Sora-Naw dude. Like im telling u. Im gonna fight u. U dont have to do anything
MX-Kills Kairi
Sora----Really dude??
US-Really dude???????
What's even crazier is going into this everyone expected YX to do the heel turn and turn out to be good and stop MX and he went out as a straight villain the whole time. Both him and Vanitias.