I feel that there's a lot hidden in that word "just". The shopping sites you have in mind, are they searchable using google? Do they accept visa cards or paypal?

You wrote that GP "heavily underestimate DN markets by service and volume". If those markets can't be found using mass-market search engines and don't accept payment using mass-market payment services, then I think they're either nïche or you need to explain how they reached large volume.

I am not really sure where you are going at. You can very well Google this all (at least in Switzerland you find clear results) the time where onion.to was actually properly indexed in Google is over tho, but that was a thing not to long ago as well.

A crypto wallet, that connects to one of those multi Billion Dollar networks, very well could be viewed as 'mass market payment service'. I at least know more people using crypto than PayPal, most no 'hackers'.