In my opinion, it really depends on how much of a comment purist you are. In practise comments tend to be more speech than prose, and as such in their purpose they may straddle the line between different kinds of "acceptable comments". It's not black and white, and they do come in different variants.
One kind of "inadequate answer comment" is "Have you considered X approach, because it seems like the obvious answer but you did not address it in the question." That can be considered a request for clarification, not an attempt at actually answering the question; a reply from the OP in the form of "No I haven't, please elaborate!" would elicit a full answer. Of course the only reason that kind of comment is necessary is because of the inexplicable rule that you are not allowed to explain the avenues you have already considered in the question itself, requiring this extra step.
Other "inadequate answer comments" are pure suggestions, but they may be sourced. "This book/study/website/movie addresses your concern, it suggests X." Such a source could be the basis of a full answer, but sources tend to be open-ended and let someone decide their own answer creatively. It's reasonable to want to just give the questioner that extra factual or creative input without feeling confident to make a deciding call one way or the other. That would rub against the "suggest improvement to question" bucket of acceptable comments.
A third kind is the kind you were talking about; OP asks for hard science, potential answerer cannot really deliver that kind of answer, but can offer suggestions that could help either the OP or future answerers. I think that those comments still have value, but I can see that they could be considered clutter, particularly if they come in great numbers. If I were a moderator (I'm not, and I probably won't ever be given how unorthodox my views seem to be), I would make a judgement call based on how many total comments the question has gotten. Removing a lone comment on a question with twelve views and no answers would not be worth the effort to me, and it would deprive the unfortunate OP of the little engagement they got.
And a fourth kind of "inadequate answer comment" that I have come across is framed more as an attack or frame challenge on the question than as an answer. Once more the lines are blurry; some of these are "your underlying assumption is wrong, here's why" (which can be considered a "suggested improvement to question", one of the allowed types); others offer a full answer to the question but often phrased as if the commenter knows it is not the answer the OP was hoping for. Since frame challenges are considered acceptable answers, I think these comments should be held to higher scrutiny. Particularly since comments cannot be downvoted, and challenges are direct confrontation with the OP, and should absolutely be susceptible to mass downvotage if the community finds them unfounded.
Those are my views, and I won't hold it against anyone to consider them wrong or think me a chatterbox. I know I don't make or enforce the rules, but I for one am happy that in practise the Worldbuilding.SE community has been more comment-tolerant than other Stack Exchanges. This site has much more creative people and a subject that lends itself better to conversation than the purely factual pages. My best engagements on this site have been comments, not answers. And until the chat feature starts actually functioning, I don't think that moving comments to chat is doing a favour to anyone.
