There are two questions tagged comparison: One question is about the comparative, for which comparative-degree is already used, and the other one is about the differences between "more than," and "more than what."
As I understand it, we can't actually delete tags - all we can do is remove any links to an unwanted tag, and wait for the system to remove it as "unused".
I suggest we re-tag the existing questions linked to comparison, and hope it goes away. If not, we can try to make it a synonym of comparative-degree. But from what I recall, your options re voting on synonyms are severely restricted by the need to have upvotes in the tag(s) you're trying to change. So it might need a mod to deal with the matter.
My position, obviously, is that comparison is at best only useful as a synonym of comparative-degree, and I personally would like to see it disappear completely. We should use tags like metaphor, figurative, simile for "comparisons" that don't fall within comparative-degree.