Shyvana and Yi don't need increased AP ratios...
Shyvana and Yi don't need increased AP ratios to make guinsoos more attractive. Stacking guinsoos 6 times on a squishy Yi build will never happen, and Shyvana has no AS steroids and her Q does not stack guinsoos which is why no one built guinsoos before the nerfs to it either.
Yi doesn't need to deal more true damage than he was before his nerfs. He needs his ult nerf reverted, that's it. The E nerf being reverted would make crit builds less awkward (Zeal items don't affect E) but I can see it causing problems in the future if on-hit/bruiser itemization gets out of hand again.
Devourer junglers were fine before sated was released. When you had to nerf 2 champions that were balanced for 3 seasons
, that should have been an indicator that you done fucked up somewhere. Bloodrazer is currently a bit weaker than old (Pre-sated release) devourer, so just revert those champions nerfs and put them at the same strength that they were at before all this bullshit.