What was achieved by giving On-Hit junglers AP ratios?
In patch 6.10 Master Yi, Nocturne, and Shyvana were given AP ratios, or had their AP ratios increased. The rational for this was that these champs should benefit more from incidental AP on items and from buffs such as Baron buff, and to lessen their weakness against armor. The underlying rational was likely to make Guinsoo's Rageblade a more palatable purchase on them for the Phantom Hit passive; as these champions don't make much use of the AP on the item.
Since then, in patch 6.13, Champion.gg shows that none of these champions are commonly making use of Guinsoo's Rageblade. This is likely because Guinsoo's has become an expensive luxury item. Given that, the only AP these champions get is from the Natural Talent mastery, or Baron buff.
The AP buffs for Master Yi, Nocturne, and Shyvana don't appear to have benefited these champions in any way. Shyvana's and Nocturne's win rates decreased, while Master Yi's increased by about 2%; likely in thanks to the buff on his E. This to some degree illustrates how ineffectual these AP ratio buffs were.
While the AP ratio buffs certainly haven't done Master Yi, Nocturne, and Shyvana any harm; it's doubtful they were in any way successful. Another kind of buff could have been much more successful, such as increasing their synergies with on-hit items in some way. This feels like a very weird change that Riot simply forgot about after it had no effect. I struggle to see what was actually achieved by these AP ratio buffs.
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sounds kinda fun :P