I'm very mixed with this one. The song itself at its core is wonderful and possibly the one I like the most from EN so far, but there are some questionable mixing/vocal direction (mostly you have highlighted) that kinda ruined it. However, the biggest missed opportunity from me is the lack of one more chorus while all of them sing together. Maybe I'm too used with how JP and especially ID make their OG songs, but this one feels too unit-centric for a branch song. Final chorus where they sing together will fix it, but alas there's none. What a pity.
The opportunity U mentioned, yes for the purpose of the song, it wud make it sounds more complete. But I also get this feeling of when a song is not complete, it gives more replayability.
Counterpoint: holoEN Mind Craft cover. final chorus is not sang in unison. But IMO it has better arrangement than this and the feeling you're describing is something i felt in that cover song, despite not having a final chorus spectacle. If you're gonna ask me, i think they're pressed with time to arrange the Breaking Dimensions song meaningfully. Bae herself arranged the singing parts of the Mind Craft cover which took her a couple of months to do.
I'm wondering if there's a space for Justice to be added to it, as Justice will have 3D's eventually and BD will be sung at future concerts. They'll probably add in that final chorus then, maybe?
It’s set up this way so they can add future generations without having to change too much. If they add a final chorus, they’d have to re-record it every time.