Do any mages beside Katarina snow ball hard?
title
title

But both her and Kat are more of AP assassins than mages.
this is probably the best answer because she has a similar attack pattern to katarina's. At least more similar than the likes of a ranged AP mage.
Like, all of them. Once mages start getting ahead getting caught in one CC ability can mean instant death.
examples.

Right but if a fed mage get CC they die. IF a fed tank / ad / adc they live and kill the team.
oh boy is it fun to play as a fed azir
Can hard carry IMMENSELY. Once you get ahead all you do is go to another lane. Bomb them and take their tower. Before you know it you've gotten 6 towers in the first 20 minutes of the game.
https://image.prntscr.com/image/G4KfMfxKRHqJOUSGevY7qw.png
https://image.prntscr.com/image/CKVzqcxJTaubDyyBvl8E3Q.png
In both games I pretty much single handily take every tower. If you miss your abilities, well that sucks, but the enemy will not be able to keep up with the waveclear.
I wouldn't call Katarina a mage, but yes there is
who is ....even easier to play. xD

Try diana and go a ap/as build and you can snowball hard af and kill towers faster than anyone else in the game