[JshWright]

In which case is it 3.6x higher?

The most common drug people get arrested for is marijuana, and the difference in use (even by your chosen metric) is nowhere near 3.6x.

The only drug where you can make an argument even approaching 3.6x is crack, which is a relatively small percentage of arrests.

I also note you omitted the "stimulant" category (which in the 2011 dataset covered methamphetamine).