Diana is still weak.
Just because a champion can one-shot you, does no mean they're OP.
Mid 49% WR Jungle 47% WR
The problem with Diana is her late game. For a champion with such a trash early game, her late game is pretty much just as bad. Diana's cooldowns mean she can only combo once per teamfight - and if the enemy have half a brain, they'd easily be able to negate Diana's dmg via lulu/Janna protection making her completely useless.
Now, say she does get a kill. Then what? She relies on her team to follow up and save her, but 90% of the time she'll get cc'd by the 4 other teammates and killed.
I compared Diana's dmg with Katarinas in Practice tool. At full build, Kat does 5k AOE dmg per combo at 1k DPS, whilst diana does 3k per combo with 600dps. Funniest part of it all? Katarina is an "Early game champion". lol.
For a champion that can't do crap for 16 levels, her lvl 18 is almost as useless.
and that was BEFORE the rageblade changes.