how is kai'sa balanced?

i wanna know what the actual fuxck was going on in riot's heads when they decided to add this absolutely braindead and overloaded champion to the game. she has a shield and a dash in a single ultimate, as an adc. SHE HAS INVISIBILITY AND MOVESPEED, IN ONE OF HER BASIC ABILITIES, THAT'S ON A 14 SECOND COOLDOWN, VAYNE GETS LESS THAN THAT IN HER ULT. and don't even get me started on her damage.
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