Of what? I don't understand "pop".
A small percentage of DEA arrests? Of convictions? Of incarcerations? Of tons of seizures? Of dollars of seizures?* Of their overall focus/effort?
99% of marijuana arrests are made at the state or local level. Look at the DEA budget and you'll see that about half of it is for drug awareness/education and anti-drug advertising and the other half is for drug interdiction at our borders and overseas.
You can pull marijuana out and it wouldn't change a thing at the federal level.
If marijuana were legalized and regulated, I would posit that the number of DEA agents would increase to prevent marijuana exports to other countries. In addition, I agree the BATF would expand -- to the BATFM to monitor marijuana retail licensing and growing operations.
Financed by marijuana taxes, of course. But those agencies will grow.
* Marijuana represents about 15% of what Americans spend on illegal drugs.