User blog comment:Emptylord/Class Reworks - Itemization Follow-up/@comment-5035765-20160512211319/@comment-1330314-20160519212639

I'm not distracting from the point, I'm fully aware that mages have occasionally been too strong in bot lane, but I also acknowledge that those times were temporary balance upsets that were easily fixed afterwards, and the design changes that brought them up ended up making the game better overall. I think the same could apply here, and I think it's ridiculous and counterproductive to oppose a design change simply because it might incur a balance upset. If Riot followed that philosophy, the game would've stagnated and died long ago.

Please refer to LoLKing and champion.gg for the main builds of every single champion you brought up. They're all AP, and the closest to diverge, Jax and Kayle, are more on-hit/attack speed focused, where they'd easily benefit from just full AP. Arguing that AD "isn't wasted" on their kits is a weak argument, since AD by nature will always allow any champion to deal more basic attack damage; that alone isn't enough to justify its purchase, as the distinct lack of AD items on the vast majority of those champions proves.

Putting aside the numerical example I just gave you of how Transmutation could significantly help a burst champion recover after their main combo, my point is that Transmutation's healing cannot activate at full health, so whenever you make use of it you'll be fully making use of the healing. By contrast, the spell vamp for Omnivore is always-on, meaning it will be wasted while using abilities at full health, and due to being balanced around 100% uptime, cannot be as helpful as it could/should in helping rotation-dependent champions heal themselves.