Be careful about Kayn buffs, Rito.
I've got ~35 games on Kayn so far. I know it's not a lot, and I know I'm a silver scrublord, but blue form isn't dramatically weaker than red form, it's just harder to pull off -- red form is just much easier than blue since you heal so much and have CC. Blue form you actually have to be intelligent about how to engage, and you can't take on entire teams at once unless you're massively fed.
If you're going to buff Kayn, leave red alone, it's fine as it is. If you want to buff blue, don't straight up buff his damage, since he already one shots squishies, but maybe increase the speed of his Q or lower the CD on his E while in blue form. Would make blue a bit easier to pull off, and close that gap between the two forms a bit.