I have never been a fan of any conlang with a comparative case. In retrospect, I think this is a result of conlangers never thinking such a case through. There are many questions such a case raises, and any description of a comparative or equative case needs to answer.
Comparisons can relate to many things. Comparison can relate to subjects' activity:
John carries more illegal merchandize than Frank
It can relate to objects' affectedness:
Erin studies more hard science than humanities
It can be more complex than that and relate to both subject and object:
John carries, by weight, more potatoes than Frank carries carrots
generalizes to "John carries more than Frank"
We can also have things like
Evelyn gave Tim more help than (she gave to) Phil
Evelyn gave Tim more help than Phil (did)
Now, let's consider how this works out with a case corresponding to "than". We note that such a case would normally not be assumed to be doing any Affixaufnahme. Such a possibility obviously exists, but needs to be explicitly stated in a grammar. However, let us assume that the comparative case does not explicitly state any information that relates to syntactical function of the noun, except that it somehow fits in a parallel slot to something in a nearby VP.
So, essentially, the comparative case locally is also a nominative, accusative, dative or whatever? Now, in some languages, undoubtedly, there are restrictions on what even can be compared, and I think I've previously mused that I bet this follows a very similar set of restrictions as that of relative subclauses, i.e. if a language permits comparing obliques, it permits comparing indirect objects; if it permits indirect objects, it permits direct objects, etc - but I also imagine it might follow very different restrictions? However, we could introduce some quirks here: maybe the comparative case is underlyingly an absolutive case in your conlang rather than a nominative. (Or, as might be even more likely, underlyingly nominative if the language is ergative in alignment.)
Thus, for the underlying absolutive:
Bob.nom is smarter Adam.comp := Bob is smarter than Adam (is)
Charlie.nom likes Deborah.acc more than Emma.comp := Charlie likes Deborah more than (he likes) Emma
The underlying nominative situation in an ergative language will be rather boring to describe, so I will skip that.
Now, how will we construct the situation where two persons' likes for a third one are compared? Maybe a voice? Maybe just a voice marker existing somewhere in an odd isolation?
This really isn't even an attempt to answer any of the questions it could raise, it's rather meant to ponder as to the questions it could raise - really, I want to know what questions it could raise.