My take is that turning the ATF into a department within the DEA is fine as long as they stop making up bullshit rules and regulations on the fly.

If they lose that mandate and we see the deregulation planned take place, then this makes more sense.

The "ATF" department would focus on tracking down the source of weapons that the DEA confiscates. ATF department would also perhaps focus on Arms trafficking where there's usually other criminal overlap, where there's arms shipments there's probably some drugs or other crime not far away.

Alcohol bootleggers/smugglers etc which might fall outside the DEA's reach, ATF department would gain access to those resources in that part of the mission.

And I mean, alcohol is a drug, so there's that too. Tobacco I dunno about but the other 2 letters make sense at least at face value. I never heard about a rogue tobacco or cigar operation getting shut down.....