[quote=@ImportantNobody]
Transformations could be a major weakness doing it my way. If your trasformation is what is compared to the opponent, getting knocked out of your transformation messes up your chance of winning while the opponent doesn't need to stay transformed. Plus for story purposes they could be caught un-transformed or can't for some reason.
[/quote]

If a transformation is wholly positive it doesn't make sense from a story sense, nor is it really suitable for Arena.