While Comments are properly used to make clarification requests and tangential observations, not answers, and Answers should provide solutions justified by mathematical reasoning, I fear the proposed deletions of Comments are an invitation to "throw out the baby with the bathwater."
As I've previously stated, if someone feels I've given an answer in a Comment, the OP or another community member should feel authorized to post an Answer based on my Comment. This often happens when I've suggested an interpretation in a Comment that leads to a quick solution, based on the uncertainty that such a short treatment would really address the OP's problem. I justify such an exchange as a request for clarification, and I'm willing to "risk" that others will capitalize on such a request to provide a good Answer.
More crucially how would the proposed deletion of Comments be moderated? We cannot individually delete Comments, but must rely on flagging for Moderator attention. There would be no queue to review such flags, and thus it will ultimately require the Moderator to judge. Of course once an Answer is posted incorporating the information in the Comment, then a good argument can be made that the original Comment is obsolete/no longer relevant.
In general my feeling is that many Questions are in need of improvement before being suitable for retention on the site, and a certain amount of discussion in Comments has to be tolerated to bring them "up to snuff", e.g. adding suitable context.
I'm also sympathetic with Questions that provide context that comes agonizingly close to a solution. It seems to me that "hints" to close the gap in Comments are preferable to "hint" style Answers. Nevertheless the Community winds up tolerating many such Answers, and it should not (in my opinion) be a rationale for deleting (or forbidding) equivalent Comments.
Ultimately I prefer detailed Answers for all valid Questions because of the benefit to future Readers.