Yoko's matter form is also fully animated for battle too. You can see if you mod her in, when she uses her signature move, the wings that she only has in their matter form are specifically animated to disassemble and reassemble
https://youtu.be/kl8noI1iDo4?t=28
Which means they cut these forms being playable in vanilla V, then considered adding them AGAIN for vengeance far along enough for them to animate Yoko's... only to cut them a SECOND TIME.