I'm going to ignore Stack precedent for a moment, and come back to it in a minute - it's not enough to say, "this is Stack policy," without investigating whether and why it might make sense to apply in this context. I'm not typically one to blindly follow policy, especially not when it asks me to remove information that doesn't exist elsewhere, so I am happy to go into more detail.
First, consider the difference between:
Probably overreading. Plato's ideal-transcendence can't be reduced to a quantifiable dimension.
It may be helpful to start by thinking about whether Plato's ideal model can be reduced to quantifiable dimensions.
One comment is "clearly" an "answer" to the question. The other is "clearly" a signpost, or a helpful remark for future answers - a note about content that might be relevant or helpful. But they both contain exactly the same information. So let's ignore the two words that frame the comment like it's trying to be an answer, and focus instead on... well... what it says.
And when you look at it without that frame, even you've left a lot of signposts like that - comments that contain only directions or references for where one should look or start thinking. You're not the only one: they're very common here. And as far as I've seen, they can be very helpful in guiding answerers in navigating topics that are not necessarily simple or easy.
The comment you flagged was originally posted as an answer. I had converted it to a comment because it, well, didn't contain nearly enough information to be a proper answer. But removing it outright would have deleted something that at least thrusted towards an answer, in a way that isn't available on that answer page, and can't be easily searched or found elsewhere.
So the question I ask when I see it flagged is pretty straightforward: does this comment, right now, contain something valuable? And it clearly does: both for anyone passing through, but especially for someone trying to develop a full answer, it provides a signpost that gives a direction in which to start heading. That's valuable.
But it's especially valuable on a site where answers are often hard to build. It's especially valuable when these kinds of connections are not ones even any mythical expert is necessarily going to see. And up until someone posts an answer that develops the point, the comment contains no redundant information, and serves only to help the reader.
Once an answer is posted that contains and expands upon the information in this comment, or when the question is generally sufficiently answered, I'd say it becomes redundant and should/will(?) be removed.
On a policy level, this is not as clear cut as it seems. I would place this under "minor, but transient information." It's minor: someone's smacked a signpost into the ground, as if to say, "try that way, maybe?" And it's transient: it will only stick around as long as it remains non-redundant.
Even that equivocation aside, we as a site can't blindly follow Stack policies. We have to be judicious about what we do and why. We are both different and unique as a site in many ways, and much of the Stack framework (and existing policy) was not set up, and will not work for us. When considering whether that policy is helpful to apply, we need to look not just at what policy says, but why it says that, to see whether it makes sense here.
While on other sites, deleting anything answer-y in comments makes obvious sense, for questions like ours, some discourse around the question is often both inevitable and necessary to build good answers. Again, once that discourse becomes redundant, it should be cleaned up.
In basically all other cases I'm totally on board with Stack comment policy. But I think following it to the letter presents an absolutist view about useful comments that isn't functionally helpful in many cases - for us. (I'm also not convinced this is against Stack policy, anyway.)