I would expect that the Wolkenritter would only be one growth affinity below Hayate (if at all) rather than two tiers below her. That or have way more experience. At the very least, I would expect Vita to have significantly more Health than Hayate (but roughly the same Resilience). Hayate is primarily a ranged fighter, so she's supposed to be pretty squishy, but Vita is almost exclusively a melee fighter and is especially prone to continuing on even with severe wounds.
Even if they had the same growth affinity, Hayate would still be far more powerful due to the sheer potential offered by Collect and Use.
Maybe also add in that pyramid shaped barrier that Vita uses, the one that lets people enter but doesn't let people leave (from the first episode of A's)?
Also, maybe rework Vita's self-boost spells so that instead of being self-boosts with N/A for Base Damage and Magic Modifier, the spells are actual attacks with formats like "Base Damage: Caster's Base Damage * X", where X is some value that increases as the spell's level increases? The current format makes the benefit of level ups rather ambiguous. On the other hand, there have been examples of spells and abilities that don't have a level at all, so that's also an option.
It could also be that I'm rather biased, because I'd love to see a spar or fight between expies of Vita and Blanc (who is probably Judgement Drive), because they're so damn similar, and that would require them to be of comparable power.