If you are trying to say “you can use your own domain with gmail then take your own domain with you later away from gmail” the answer is yes, but you are still issued that domain from a centralized registration service and it can be seized from you and the process of pointing a domain to a new server is complicated enough that normies don’t do it

Versus taking your npub somewhere new? Extremely easy 

 Shifting the goalposts? 

 No, literally returning to my original point which you seem to have misunderstood