There was no acknowledgement by the British, that's the point you're missing. Batman had no authority from the British government nor the governor of NSW to sign any treaty. If you signed a treaty with another country would expect that to be binding on the Australian government? No of course not because you have no authority to do so.
There is no international court that has any authority on land ownership in Australia.
Irrespective of that, the treaty you refer to covered a tiny part of land in Australia with one of hundreds of different people. There is no legal standing to enforce a treaty between two parties upon another two separate parties. It's like saying if your neighbour sold his house to someone that they could enforce that sale on your house. Complete nonsense.
Finally if what you are suggesting had any legal standing whatsoever don't you think some blood sucking lawyer would have already put forward a case to some international court on behalf of the indigenous people of Melbourne?
