There is really no way to dispute the idea that indigenous people were the original landowners of the continent of Australia. It is well established that they were the first human beings to get to Australia and were the only human beings who were there until the coming of the Europeans.
Because of this, it is clear that indigenous Australians have a moral claim to the land. However, I do not mean to say that indigenous Australians should have the right to regain the legal (as opposed to moral) title to the land. It was surely wrong for the Europeans to dispossess the Aborigines by force. However, that happened so long ago that there is no viable way to undo the wrongs that were done.
My view, then, is that indigeneous Australians have a moral claim to the land since they were there first. However, they should no longer have a legal claim to all the land since that would simply be impossible to enforce.