Don't you need multiple service providers to hold your keys and sign on your behalf, basically multiple signers, these are services.

I can't imagine the UX of asking normal people like myself to sign up to multiple providers and judge who deserves my trust and who don't  

 Meh. You can just trust an aggrigator directly like on that demo-site, or a nice market place where you select your providers, pay and move on with your day should do it. 

Judging whom to trust is a problem in so many places/things yet the world still functions. 

 Me is the wrong attitude if your mission is to make public keys usable for most people. But I don't think I can offer much better alternatives given that key delegation was already rejected in Nostr before.

Diversity of experiments are good as well.