My understanding of kindness is that we are hoping to be truly beneficial in every situation, and that this desire means a whole suite of things: being nicer, sure, but also being more aware, more present, more articulate, more fearless, less habituated, etc., etc. And sometimes even being firm, or having an edge, or even being angry.
To me that really would be the essence of kindness, to have one's awareness so developed and refined that you could tell just what was needed, and not do any more or any less, and maybe not even be aware of what you had done, except it would be a helpful thing because of how fully present you were. Well, as Aerosmith once famously said: Dream on.
It's not fiction's job to be photographically representative of reality. If I want to make a fictional world where there's no kindness, this doesn't mean I believe there's no kindness in the real world. In fact, what it may mean is that I very much value kindness. Like if you make a painting in which only greens are allowed, it wouldn't mean you don't believe in blue.
As for "toothy kindness" - I think all traditions are full of this sort of tough kindness. If someone is on a wrong or dull path, and someone else startles them into awareness of that, then that's a blessing. And the method by which the startle is obtained might be anger, or satire, or an intentionally applied indifference. But that is, of course, a fine line.