Kai'Sa is at a 86% Pick/Ban rate.

Uh, where are you getting those stats from?

You weren't here when Kassadin had over 90% banrate and almost 100% winrate [slayer-pantheon-popcorn]

I checked Lolaytics and Kai'Sa starts with a 12.0% pickrate and 18.0% banrate in Bronze (all regions) and 51.7% winrate and it gets higher as the elo goes up: she has 16.4% pickrate and 61.0% banrate with 53.2% winrate in Plat.

So she will need more nerfs than the ones that are in the PBE currently imo.

You missed zoe's ban rates pre 8.4 then

Across all elo's - 79.4% ban with 20.2% double ban Master+challenger - 88.6% ban with 38.9% double ban Diamond - 92.3% ban with 35.8% double ban Plat - 93.7% ban with 31.6% double ban