Instead of nerfing the mastery or items that have caused her to be "op" Riot has decided to nerf a champion that they have not basically touched since league came out.
Ok cool. A champion with horrendous mobility issues, horrible mana issues and long cooldowns without blue buff.
The nerf makes sense using this train of thought:
Problem: Her Q/E and R/E combos are too reliable for the damage they do.
Potential solutions:
Nerf the damage, but keep the reliability. Consequence: You lower the reward for playing Anivia well. Meh.
Nerf the reliability, but keep the damage. Consequence: She keeps her reward for being played well. Her core combo remains as powerful as it is, but edge cases where she barely tagged you with Q or R at full range and still got a full-power E off are removed. Feels a lot better to play against (less bullshit), and solidifies her mid-long ranged character. Remember, unlike the other long-to-extreme range champions, she has no mechanic that makes her come closer to you than necessary.
Overall, after giving it some thought, I think that this nerf is a good nerf that keeps the core character intact.
From playing Anivia myself, and one of my friends thinking he is Froggen junior, I know that the window during which you can combo an E onto R or Q is sometimes rather BS. Example: Hitting someone at full range, taking a moment to decide to move in to E, barely getting in range due to the slow with the target in retreat after the stun, enemy is still moving away while E is in flight, but takes the double damage because the window for it is so long.
Anivia is one of the hardest mids to master if not the hardest mid to master (Azir is another contender for this spot). What reward do I get from playing a champion that takes so much time to master and is singificantly harder than the many easy mode alternatives I have? Anivia has horrible mana issues, no mobility (in solo queue you have to follow the enemy mid laner when they roam), and long cooldowns. Her farming pre-6 is extremely difficult even for mage standards. She gets knocked out of her ultimate if she gets sneezed at. I mean... come on, and then this nerf? You have to understand why this is so upsetting for Anivia mains.
Also they nerfed warlords bloodlust for trynd but they cant nerf a mastery or an item for anivia and the other mages that benefit from whatever it is that suddnely made her "OP." lol...