And even if a single mint can scale to multiple servers that already does what tether or any other crypto currency claimn

Claims to do *

As far as I know (haven't looked into it in awhile) this is not accurate. Your wallet can have ecash from multiple mints, yes, but a mint operates by itself ("single server hot wallet"). fedimint expands on the concept, requiring more than just one machine, thus enhancing reliability and security.

Single mint doesn't mean single server just so you know.