I tried operations like revoke with https://beta.steemconnect.com/revoke/wherein-io, and it works well.

However I think I understand now the point is that, since steemconnect-api is highly centralized, the owner of https://steemconnect.com can easily control which chain its users (e.g. users of busy.org) will interact with, by updating the STEEMD_URL environment variable in the steemconnect-api project: https://github.com/ledgerconnect/steemconnect-api/blob/master/.env.example

So the same should happen to SteemLogin to switch to another STEEMD_URL