Comments are to request clarifications, yes. But not only, not really
They are also commonly used to point out related issues. So pointing out general patterns in OP questions is not unheard of, and I believe pretty valid. Linking questions that are not duplicates, but somehow related, is valid as well.
Basically, the main question is: can this comment help make this post better, or help author to post better content in future? - if yes, then great! If no, then it probably should be removed (or not posted in the first place). But if comment is helpful and constructive, it does not have to be strictly on topic of this particular question.