I think the issue and again I think pay to win has different definitions in my opinion for retail and classic.
For classic gold rules everything. In that sense you have:
Seller.
Buyer.
Gdkp.
Boosters.
Then the gold goes back to the sellers, since they are the primary boosters.
In retail you can legit pay to WIN.
Want glad? Pay gold.
Want to full clear mythic raids? Pay gold.
Want to run any mythic+ for titles or achievements?? Pay gold.
Literally paying to WIN. Because most players can’t do that, because they aren’t good enough.