“They absolutely do have the power to regulate firearms in the US.”
Well, go ahead and cite the ATF powers to write laws in the US Constitution.
I’ll wait.
They get their authority from Congress who unconstitutionally give MANY government agencies the power to create “rules” with the weight of law.
While my opinion appears to be the same as yours, which is that these measures are defacto unconstitutional, and that these federal agencies lack the authority under the constitution, they still have the power.
Observing that something exists is different from endorsing it.
It is an objective fact that if this regulation is passed, an entire class of pistols will suddenly become NFA regulated firearms.
If it was up to me, the NFA would be repealed, but it remains the law of the land, with all that implies.