Hmmm... always liked Q, he is all you said, but...
We, meaning the federation in general, or the enterprise/voyager crews in particular, learned from those encounters, and he has helped.... as bad as the borg were, how much worse would it have been with no notice? I think it mostly he plain can't think like us, so is not limited to our responses
I've not watched Picard series though except some choice spoilers on youtube... so cant say too much on it.
I'll probably eventually buy that series on dvd/blu ray.