That's an entirely different argument and completely irrelevant to the use of VAR. It's there to help make a decision in applying the rules of the game, not to change the rules of the game.
It depends entirely on the tackle. In this case the Aussie player tackles from behind, gets minimal contact with the ball which then comes back into the attacking player's possession. He then trips the attacking player from behind.
It's true he can't just disappear but it is his decision to judge whether he can execute a legal tackle from the position that he is in without fouling the opponent. Maybe he thought it was 50/50 and it was worth an attempt given the situation.
Yes, football is a contact sport but trips from behind have never been legal. It's entirely valid to say you think a rule has no benefit or actively harms the game but that does not make the decision wrong in this case. The correct application of a rule you view as dubious is still a correct decision.
And no, it is not a foul according to me. In this case it's a foul according to the rules of the sport.