Different stacks seem to handle this to different degrees.
I recently flagged a comment made under a question which was clearly meant to be an answer; after three existing answers had already been submitted.
I also commented under this comment to the effect that the comment space should not be used for answers.
My flag was declined and my comment deleted.
Since then, yet another comment has appeared, which also should be an answer.
This makes it seem as though answers in comments, completely bypassing the voting structure, are perfectly acceptable.
Is there consensus for this stance?
My own personal stance on this is far better reflected by the policy on Photography SE Meta - Please put your answers in the answers section, even if they're short
Of course, we're all tempted to drop in short comments when a full answer might seem too much effort, but when the points raised are already in the existing answers, this seems a more deliberate bypass of the voting structure.