Anivias laning phase is just... stupid..
Takes about 60%+ of your health instantly with QE at level 2
You somehow manage to kill her? Nvm she has two health bars and you only have 6 seconds to kill the second one (and nobody else can 100-0 someone in 6 seconds before levels 8-9).
All-ins you at level 6 with an ult, a wall to keep you in, and another 60-70% of your health QE burst
You burned flash and escaped? Doesnt matter, her ult is on a 3-second cooldown and she'll do this again immediately.
Maybe she roams bot and gets a free double when their flashes are down (because nobodys escaping anivia without flash if she uses her wall competently.)
her costs are still so high that she'll easily run out before just about any common mid pick. Oh and of course the fact that when she's building mana her opponent is building damage and can burst her down without a hitch.