Simplest solution would be to just have the wyvern part of your soul like it is in almost every other instance of dragoon ff related or otherwise. To only come out as animations during buffs and attacks. I would rather be dragon-like myself than have one linked to me draining my power. Legend of the Dragoon like transformations as a high lv buff <yes, please>

Even if hate was linked to you it still doesn't change the fact that on big mobs your damage would be gimped because you're essentially giving up a noticable % of your power for a lower level companion who's stat's won't do crap against HNMs Gods etc...