Is Australian accent a moderate between British and American ones?

Like the others said. There is a split between American accents and Commonwealth accents, with American often more archaic; the retention of r after vowels is the biggest shibboleth (and several British and Irish accents line up with America there). The Australian accent is pretty close to London English, though apparently there was a Midlands influence too.

What is halfway between British and American is not the accent in Australia, but the spelling, and increasingly the vocabulary. We spell jail not gaol, for example, and you will hear more and more US-specific words. As much as anything, that’s media and globalisation.