requires too much set up.... he clears the board and your opponent gets 20pts.... you then have to overcome that, either via earlier setup, or 2+ card advantage (and more pts)
I am not embarrassed to say that I got sucker punched with Kambi by a CA Shupe deck in casual... I was up like 160pts, despite being several cards down... couldn't figure out why the other player didn't just forfeit... played my last card secure in my upcoming win... boom: Kambi.... I was laughing my arse off that I didn't see it earlier.
Not even i'm using Kambi now, as it's really hard to pull him off now, since it requires extreme CA for R3, which is extremely hard to pull off on SK. I did try a Shupe deck recently, with "Kambi carryover" with the Prize Winning Cow (Harald Houndsnout also a possibility), and Dudu to copy Hemdall, plus silver spy and Shupe to hopefully draw 2 cards on R3 and get CA, but it's extremely difficult to get there, and lacking a big 1 turn finisher.
I used to have a QG + Kambi deck, and spent the whole match building them up to pull 40 pts with 4QG and Cerys after Kambi, but with the power creep situation while these units remain the same, it's impossible.
Kambi just really needs a lot of planning to get that card to work. Not much else to it if you don't have something planned out. Like a full Queen's guard res + Cerys or a strong removal + card advantage.