It's not possible to get used to such huge latency (500ms). He is a burden for a team in competitive games. It is a fact (if that "friend from Australia" exist at all).

That friend certainly exists and he's not a burden on the team. Maybe you focus too much on the latency number and forget that some people play to have fun, while still playing very decently.

I think it's very rude you suggest I don't know people in Australia (do you even know someone from Australia?)

Still I don't believe you. I have experience of playing competitive shooter with 250ms latency and it was nearly impossible to aim. And you are talking about 500ms latency. Let's just agree to disagree.

Well, he plays with between 100 and 300ms latency on average, atleast whenever I check the player screen. They're perfectly capable of hitting targets reliably.

On a similar note, I used to play World of Tanks with around 400ms latency before I got a better internet uplink, while it's certainly bad for a month, you start to get used to it eventually and the brain compensates. Of course, if reaction time matters you loose, but you can adapt your playstyle in a lot of games so that pure reaction time doesn't matter as much.