> It’s basically like saying the state of New York could have been able to drive COVID down to zero while other states had it exploding.

This is exactly what Western Australia did. The Australian response was not nationally coordinated and each state has been doing their own thing. They have land borders between each other and yet the Victorian outbreak didn't spread to either NSW or SA because they implemented border checks by lining the roads with police and fining people who attempted to circumvent them, while WA implemented a hard border even earlier as soon as there was a non-zero number of cases.

The Australian states are geographically larger than many European countries, so I don't think it's that it's an island. The only effect nationally was hotel quarantine for arriving flights which is possible for landlocked countries as well.