The reasoning behind why Anivia's 2 ability combo is so much more out of hand than other mid's

I could name a plethora of mid laners than in two abilities can chunk an insane amount of health. Just off the top of my head . And that's fine.

The problem with the anivia combo is there's literally no counterplay.

People developed the R after E to signify even less counterplay in reaction time, and it to be more accurate because you literally just drop it on top of them. The problem is there is absolutely no counterplay to E.

You can't dodge the extra damage, because the catalyst isn't there yet. She can put it a single frame before the ability hits, doesn't matter, there's nothing to dodge.

The cooldown on it is so low that you cant punish it, you're already at half health, going in means by the time you want to back off it's up again.

It's a point and click decent range fast travel speed spell. The catalyst is an instant cast aoe placement that brings the entire combo down to absolutely no counterplay.

You can't even spellshield it. She just places the R so that it gets an extra tick, and the first tick procs the spell shield.

There is literally zero counterplay to this combo other than "Don't be in range" which is NOT COUNTERPLAY. You can make a champion that INSTANTLY KILLS PEOPLE on melee auto with .1 attack speed, staying out of range still isn't balanced counterplay. That's literally everyone in the game.

Even the champions I listed there is counterplay. Veigar has two delayed AOE's, a skillshot, and his ult. Well you can't avoid his ult, you just have to spellshield or tank it. But you can properly avoid W and E and sidestep the skillshot.

Viktor has the Vector casting, so it's gonna be difficult to dodge, but you can. Q's full damage requires it to be hit and auto attack, but it is point and click, and his R is instant place AOE, but it also doesn't have an 8 second cooldown.

Nidalee (As much as I fucking hate her) has to hit a slow moving narrow skillshot, then risk her life by jumping into melee range with her mobility to get the kill.

Anivia, you just do....nothing. There's literally nothing you can do to avoid her combo besides not being in range. She has to mess it up herself.