I always think it’s funny when people go around saying their statistical methods have some sort of “guaranteed” performance. I mean, sure, guarantees are fine—but a guarantee comes from an assumption. If you want to say that your method has a guarantee but my method doesn’t, what you’re really saying is that you’re making an assumption and I’m not.
Assumptions are fine—they’re necessary—so that’s all cool. Let’s just remember where guarantees come from.