Onion sites are not as resistant as you may think. While you have a point, there would need to be a massive amount of onion relays to make it work. Something I'm pointing out for a long time - a decentralized swarm. Make relays as easy to setup as snowflake proxies. Make onion addresses ephemeral, rotate them, add multiple network paths, etc etc But decentralized networks are not an easy beast to tame, they behave like a living organism with their own rules.