It's only an anecdote but I used to buy Adderall on Libertas, which was a Monero-only drug market, seemed to work pretty well and solved a real world problem for me.
I run data collection scripts on 64 different darknet sites. Markets that accept both BTC and XMR get hardly any XMR deposits, WHM is a major market that makes up essentially all the XMR traffic but is growing much slower than BTC-accepting markets despite being very popular on Dread.
At least 90% of darknet trade happens using Bitcoin.