Yeah, I know, I got ambushed.
The problem I have is that I took it to a LGS to swap out the birdcage for a brake/suppressor mount, and the barrel extension broke loose before the flash hider. Got it back together, but couldnt get the FH off.
Can any other TA owners confirm that the FH is not pinned and welded on a 10.5" barrel?

Thankfully, I didn't place an order from TA...

Tell your LGS using a set of barrel vice blocks would have prevented the extension from turning, they should have know better than to use a reaction rod or upper receiver block for FH work! since the extension turned, unless they torqued it back to the exact same spot(unlikely) the head spacing has been change.. make sure your LGS checks head spacing! If the barrel is melonite treated it was probably done after the extension was installed, a known no-no and contributing factor to the extension turning along with improper FH removal.. your probably better off replacing the barrel.

As for the FH, is it an extended type that brings the barrel length to 16"? if not, I see no reason to pin and weld the FH to what would be an SBR/pistol barrel. More likely, TA used some form of thread locker, IF, it wasn't just the improper barrel treating/FH removal that cause the extension to break free before the FH in the first place. PROPERLY secure the barrel, if the FH does not turn off easily, heat the FH and it should twist right off.

getting the headspace right and barrel extension torque is one problem, getting the gas port to align with the barrel extension pin is another problem. getting both problems solved at the same time is highly unlikely.

No need to shit talk the reaction rod/receiver blocks. The reaction rod was specifically designed to be used for changing muzzle devices and it works well. The only cases where people have issues is when they use low quality, or bad parts. I don't know of any muzzle devices that can bring a 10.5 to 16. The longest I know of is 13.7 to 16 so pinning and welding is a nogo. Was the barrel melonited? If so there have been issued where barrels melonited after the extension is torqued down coming apart due to the heat treating. If the company you ordered from aren't total idiots they wouldn't have put thread locker on it. I've only heard of one case where a loose barrel extension was fixed, and the manhours/effort put into it was way more then a replacement barrel would cost. OP your barrel is a paperweight, id recommend an upper from a better manufacturer (ie DD/BCM). Good luck.