As far as the credits on the Itunes music goes, Mizuta only has two tracks credited to him (Maelstrom GC & U'ghamaro Mines). Majority of tracks are composed by Uematsu, with some of the newer stuff by Soken. Tanioka, as far as I can tell, has not been involved with XIV. She hasn't been around for XI for awhile either.
Uematsu was hired to compose all the tracks from the start, but obviously, he wasn't hired for the long-term of this game, kinda like how XI is. Uematsu scored the initial tracks, then Mizuta and Tanioka took care of the subsequent updates.
On a curious note, Mizuta has called his new band the Nana Mihgos.![]()