I think you're right, and do you remember a couple of years ago when the ATF came out with a ruling that if you shouldered a brace then you 'remanufactured' the braced pistol into an SBR and was in violation of the NFA? The ATF caught so much backlash over that that they withdrew the ruling.
The ATF knew they made a big mistake with their original SIG brace ruling, and have been trying to walk it back ever since, but the braced pistol market exploded on them to the point that I think it's too late to put that genie back into the bottle.
If we’re relegated to accept the SBR designation and all that comes with it, making a stand on a “pistol brace” that circumvents the stamp and hoops one has to jump through isn’t the hill to stand on, IMO.
Personally? I think the ATF should be disbanded and demolished and no restrictions meted out on 2A weapons but that’s not our reality.