The best passive ulti?

I think you still misunderstand me. I said Kunkka doesnt build AC or Drums unlike other cores. And 3 STR gain may be high, but heroes like PL or CK still outtank him by far, because they can spawn illusions.
Other cores like Tiny or Ember can build Drums to boost their HP and they can deal more consistent damage.

Currently Kunkka is too weak as a hero whcih is why you will never see him drafted this patch in the pro scene.

My vote would be grow!, would be incredible on a Luna, when you think about it...

My vote is for Multicast

I really like Juxtapose but I also really like Desolate and Untouchable

Those aren't ults, though.

Actually Juxtapose is an ult now in 6.82

He has never been weak, even if you go "safe way" of double Daedali, or Daedalus+Abyssal, etc. he still can dish out high damage, which makes it much easier for main carry to do the job. Out of semi-carries he has the highest damage output, comparable to that of Ember Spirit. He is strong from his level 6 till enemy carry gets too fat for him to notice Kunkka, and that's, like, the whole game.

And 3 str is not enough to tank, true, but he is not supposed to tan damage he is supposed to dish it out(at least when we talk about Rapier Kunkka). Try it yourself, with enough awarenes and game sense he works wonders.

I played him enough to warrant him being strong early - midgame, but really crashing down lategame. If you don't get a good Tidebringer crit you lose every fight lategame and I never recommend relying on RNG for wins.

Carries like Ember and Tiny are just as strong or even stronger with the same farm and they stay strong all the way to lategame. Kunkka is a peaking hero which makes him very weak compared to the scaling carries.

Ok I'm not going to argue with you I'll just say I have enough experience with Kunkka too, and Rapier Kunkka in particular(~50 Rapier games), and withRapier I find him as devastating late game as he is eraly- amd midgame. Little less reliable(though I mentioned the way to minimise RNG influence on your result), but very dangerous.