That's not enough if land had a different configuration once upon a time.
We can also trace when the land configuration changed. You are viewing the past like
@It is a mystery , but we can track most of this stuff down like an episode of geological CSI-Miami. Everything from ice cores, to plate techtonics, to radiologic argon/potasium dating can tell us when and where land shifted. In fact, most of the continental shifting stopped prior to humans departing Africa, so land mass movement was not a factor in aboriginals or native americans leaving africa.
Now, i do concede that sealevel exposing land is an outstanding factor, but this is one of those things that the air composition inside ice sheets/ice cores can tell us more about. For example, the air has a different composition of elements at different points in earth's history; and this air can get trapped in ice at the poles as it freezes, so we can tell the level of seas by tracking the elemental components of air pockets trapped in ice at different levels(corresponding to how old the ice is) in history. From there we can use modern ocean floor mapping to tell which high elevation land was exposed during the aboriginal trek.
The prevailing viewpoint is that the continents had stopped shifting before aboriginals left africa, and that their long trek to Australia was fascilitated by drastically low sea levels, to the extent that primitive boats could have aided them in their migration. And by drastic i mean really drastic, to the tune of the ocean being more than 300ft lower than now.
And i will admit that this last point is extremely anecdotal, but the origin stories of the aboriginals themselves actually describe how low/high the sea was in their infancy to a remarkably accurate degree, which further supports the prevailing viewpoint. Their own stories have been the amusement of anthropologists since the 80s. If you dont want to listen to the western viewpoint, why not take the aboriginal's word for it?
Link->
Ancient Sea Rise Tale Told Accurately for 10,000 Years