I simply disagree. Are you actually arguing that marking 
and 
has zero value for delivering feelings because they are two reactions?
Does that 
mean /s? Obviously, sticking to categories is a structural value for sorting, but the alternative, which Discourse thankfully has, is tags. And yes, tagging of posts (rather than only topics) is a potentially useful thing. Multiple reactions (Retort style) actually allows a version of it because custom reactions can be added and labeled which can be whatever uploaded image with whatever name. For example, on a Discourse instance I use, there is a Retort reaction with the label “changed_my_mind” which really is superb to have in the options.
GitHub is another that allows multiple reactions, and it is really nice to have. There was a time when only like or up/down were common and having a variety of reactions was not a thing. At that time, having various reaction choices was just as useful as it is today, the developer/designer community just hadn’t realized it yet. Now they have, and consensus supports having a variety of reactions available. Allowing people to mark multiple reactions to one post is the same pattern. It is useful enough that nobody who gets it would want it gone, and at some point it will be consensus once everyone realizes it, and anyone doubting it today is just doing the same naysaying as people who resisted having various reactions in the first place.