Materia, in general, has been nerfed in this game, and builds are therefore less important compared to Remake. So, aside from the basics (HP Up, MP Up, Healing, and Elemental linked with an element), feel free to equip anything that best suits your playstyle. If you are completely unsure, you can refer to the Cait Sith video (th-cam.com/video/nNKuOIwLj_M/w-d-xo.html) for a general framework of what works for the legendary bouts.
Materia, in general, has been nerfed in this game, and builds are therefore less important compared to Remake. So, aside from the basics (HP Up, MP Up, Healing, and Elemental linked with an element), feel free to equip anything that best suits your playstyle. If you are completely unsure, you can refer to the Cait Sith video (th-cam.com/video/nNKuOIwLj_M/w-d-xo.html) for a general framework of what works for the legendary bouts.