JAG's aren't the convening authority. Like anyone else in the military, they're following orders. If you've got a problem with the charges (as I do), then your beef is with command, not the attorneys prosecuting the case.
There will be an Article 32 hearing, much like a civilian preliminary trial with elements of a grand jury. That hearing will determine if the evidence supports a referral to a court-martial. But, the JAG corps is obligated to hold the hearing as the SEALs have refused Mast. They aren't "pushing" anything - the Commanding Officer is.
"Only a person in their chain-of-command can initiate action under the UCMJ. I am trying to ascertain who that was or which unit the person commanded. As someone pointed out, this could have been handled with a non-permanent letter of reprimand which would not have had any professional impact......"
I have yet to find a source for the info [underlined above]. Do you have any details?
Then screw the Commander!