Fun fact, the last time Anivia's damage was directly changed was when NASUS was released. Let that sink in for a minute. If it was truly an issue, don't you think it would have been dealt with by now?
Now, here is the thing about "difficulty" rating. By your logic, all difficulty should be based on the absolute EASIEST thing to do on a champion. If that was to be done, then ALL champions would be rated as stupidly easy. The difficulty bar more or less represents the effort it takes to become fully proficient with a given champion.
Now, if you are complaining about her E damage, then let me give you the exact numbers. Assuming max rank, her E deals 175 + 50% AP, this doubles on a target with the "chilled" debuff. Even if she uses her ult + E, the damage from that is actually not that impressive compared to other 2 spell combos. Example, a Leblanc Q+W will deal more damage than Anivia ult+E unless you stand in the ult for an extended period of time.
Anivia's E trades strong stand alone strength for better synergy with her Q and ult. Leblanc Q, Akali Q, Zed ult, Yas ult, Syndra E and ult, and Ahri E are all examples of spells that alone are pretty lacking. However they become much stronger in usage with other spells.
If you think Anivia's most difficult aspect is using E with ult, then that shows exactly how little you know of her.