[Chaos]

Well, using a percentage of a user's stat is basically just using its elemental ATK at a different rate. It would also greatly complicate the damage calculation. I think it's probably more sensible to start with a scaling nerf, and possibly making Youkai skills have lower scaling when they're evoked instead of used by the Youkai themself.

That, and Slydria's scaling suggestion looks more like a buff to Youkai damage.

That being said, however, I don't think the damage a Youkai itself pelts out is the issue here; it's the Summoner being able to access the full 340% Elemental ATK scaling with boosts that pump their E.ATKs far beyond what Youkai can achieve.