I’m also the person who likes Flarum’s UI style significantly more then Discourse style (but not functionality and not community and devs support).
But exactly this item was NOT invented by Flatum, it seems similar to long-time existed “enticement to commenting” at WP and wpDiscuz etc.
So when it looks really nice and attract users to write something, I don’t think that it’s truly useful. It does not bring any additional functionality and it’s the true space wasting. At aspect of the “better offer to reply” functionality-style - I more prefer the always visible big “Reply” button above the navigation bar as at Flarum - it’s more useful and more compact at once!
Also in terms of Discourse UI there are many more important thing to do, at my opinion.
When its smart by default for most mass any-users communities with topics up to 10-50 messages… for a communities of professionals or just smart&responsible persons - it’s the opposite! The always visible big “Reply” button above the navigation bar - are really useful and obvious that it is much more comfort to start write your answer instantly after each message reading… instead to read whole topic which can have 100-500-1000-10’000 messages - by the end of reading which you will simply have forgotten what and to whom you wanted to answer… it’s obvious. Also when user start to write his answer while reading - in the course of reading user can add more other users nicknames to which he will address his answer, etc.
Current Discourse small “reply icon” is not very visual, just an icon and a little too far from the center.
It’s easy to make a such option at dashboard or as additional plugin - with it professional communities will display the always visible big “Reply/Share/Favorite/Report/Follow” buttons above navigation bar, mass mess community will hide them. Very simple, very useful.
But still I agree with your rationale that moving Reply/Share/Favorite/Report/Follow to most bottom must minimize useless parasite actions. But still at professional communities those buttons placed as at Flarum at right side and always visible - is more “visually comfortable”.