That sounds more like it!
Of course plenty of people will be rejected. But I think if you were predicted, say, A* AAB or AABB, you really wanted to try and you thought you had good reason for low predictions, there's no reason why you shouldn't.
If you had exceptional circumstances, you might try with lower predictions.
I think the problem with citing grades is, I don't think Oxbridge (or any other university for that matter) believes that a student with an A* is automatically going to be more brilliant than a student with an A or B. Of course it's a good predictor. And things get even hairier when we're talking predicted grades, not grades actually gained. So it isn't straightfoward.
We talk far less about non-Oxbridge universities, which is ridiculous, but if you look at the Russell Group, you will see standard offers posted on websites that might be AAB or AAA or whatever, and you'll also find students who get in who end up with much lower grades. And some of those will do excellently, and some with AAAA will do badly.