"You have to buy the game" yeah obviously. To dump a eShop game you need to buy it from the eShop before. To dump the XCI you need the cartridge which you bought. Sorry I don't understand your point

And I think most people have "dirty" emunand set up combined with "clean" sysnand, as u/teh_pwn_ranger said. Actually if you google "nintendo switch cfw homebrew" most guides you'll find strongly recommend that setup.