Gimpy, I don't know when you were in but across my time, 92-06, First Sergeants and Sergeants Major came from all MOSs, feeding into one single MOS 9999 that could be assigned to any unit, anywhere, women excluded from actual Victor units. I always saw a pattern of air wingers getting sent to the grunts and grunts getting sent to the wing. Helps bring the balance back I guess, but I never got it either.
Also, this SgtMaj is hardly "in charge" of combat arms units, nor is any MEU SgtMaj. I did three LF6F MEU(SOC) deployments, and hardly ever saw them at all. Certainly never saw any of them in the field, but that's just it, that's not their job. They're admin, make sure the enlisted aren't getting fucked over, keep the comms going with back home, deal with legal matters, or whatever else is needed as may be necessary. The MGySgt is the one working as the Ops Chief effecting combat operations, not the SgtMaj.
My main recollection of the MEU SgtMaj from my last pump, time to remain nameless, comes from two incidents. One where he went high and right because I EPD'd two Corporals for a couple days cleaning bilges down below instead of running them up the flag pole, and the other time when he came after my Platoon Sergeant for fucking up the biggest shitbag I ever saw (wife beater, druggie, deserter, etc.) in "self defense" of liquid courage stupidity instead of letting him get away with it. I hope this latest selection, regardless of what is between her legs, is a step up from that pussy piece of shit.
In any case, they would blow a vein if they saw us in the field, what with all the poor shaves, hands in the pockets, not wearing our covers and having dirty boots. I even walked while smoking... Oh the horror!!!