Diana needs a rework.
I think the recent buffs proved that diana can't ever be healthy without some sort of update to her kit. I'm not saying she needs a full rework like urgot, but she needs a few of her abilities updated, like Xin is getting. Diana, regardless of her winrate, is still really insufficient in games because of the lack of AP Itemization that synergise with her kit. a good place to start would be deciding whether she's a bruiser, or an assassin.