Mitron lacks the shoulder pauldrons and little wings the rest of the Red Mask Overlords have. Now the thread that pointed this out hypotheses this was because another Mitron fragment had been raised to the seat already and thus Eden!Mitron was no longer officially ranked in the Convocation of Fourteen. Which I thought made sense, until I checked back and noticed he is also missing them in the flashback where he talks to Loghrif and she on the other hand definitely has them. And thanks to the flashback images and the Ardbert echo memory, we know Mitron had the Pauldrons when he was working with Clyva and when he was killed, as seen here:

so it doesn't seem like Mitron is supposed to have a "lesser" robe but he does.
Now it's totally possible there is a story reason for this we just don't know yet, but given what we have seen, and the fact that 5.4's production was obviously effected by setting up wfh and covid, it wouldn't surprise me if Mitron's model was given the wrong robe by mistake and it just slipped through the cracks in a very hectic time for the team. Which would be totally understandable.
If the image link is somehow broken, both M and L's wiki pages have it in there gallery sections