It seems to me that it is not uncommon for a user to give what I might call a "stub answer". There are of two basic kinds: a) A resource is linked which could be the basis, or part of the basis, for a valid answer, but no write up is given and further research needs tom be done. This comment is of that type: I later built an answer starting with the suggested link. b) A response is given which could, later, be developed into an answer, but lacks cited sources and probably lacks needed research, but it can be the starting point for an answer. The second example in the question is of this type. Neither type purports to be a full answer.
It seems to me that both types of stub answer can lead to a full answer, either from the same user or from a different person. As such, I think they are are more often helpful than not. I do not see these as seriously "attempting to avoid quality control". In particularly the 2nd example above, where the same user later (after further research) posted a full answer, one that currently has 25 upvotes, does not seem to me at all an attempt to avoid quality control. I don't see this kind of comment as one that should be deleted by a mod. The fourth example is a little more dubious, but only one comment there is from a user who also posted an answer, and it is only about one aspect, while the answer from the same user is more thorough. One pair of comments there could almost be an answer as it stands.
In short, I don't think the kind of comments represented by the examples in the question really represent answers or need to be deleted by moderators.