[HYPOTHESIS] What if Anivia's damage scaled a bit off her mana?
Anivia's got massive mana requirements that leave her with really awkward low-power moments while she tries to build stuff like AA staff and Grail. Her mid-game, in particular, kinda sucks when she can't finish up AP because of her mana demands.
Kassadin and Ryze would have these same problems if they didn't scale off mana, which they do, but Anivia only scales off AP. This is one of the reasons she is considered low-tier at the moment, not just her lack of mobility.
Since Anivia has to be so mana-intensive, why doesn't she get some damage out of it? I think it'd do her some good if she lost some of her AP ratios in exchange for also getting mana ratios.
But that's just me. Anybody want to chime in?