Hum.. it has nothing to do with NIP-78 because it is not client-based. 

Its more like relay lists: you just select a few for the app to use. 

Trust is needed because they are doing the calculation for you and there is no way to check if the calculation was done correctly. 

 I don't understand how it's different, choose a host image service, Proxy user media, cache, and this would be a service to calculate your followers, zap and WoT. 

 That's correct. But none of those settings are saved on NIP-78. They have been generalized to be used by any client.