Is it best practice to revoke server permissions to the server "public" role on SQL Server instances?
Yes, you should fix this. If you have multiple DBs in the server, a legitimate user in one DB might have nothing to do in another DB and will not be a user in that and hence 'public'. Why would you give pubic user permission to view/access objects in a DB they are not entitled to?

Make sure to test the application after you fix these. Sometimes even a legitimate user might be missing appropriate grant permission and might have been working based on public Access, which won't work after you fix the 'public' role access. They needs to be granted explicit access through grant stmt to specific objects or via database roles or via user roles.