You completely contradict yourself with this 'logic'.
In the top half of your message, you note that the name of a particular school has no correlation to the level of knowledge or skill of a provider. Yet, you later make the claim that there is no other way for a patient to assess whether a provider is 'good' or not.
You are right, there will be some patients out there who will make a decision based upon the schooling of a provider - just as there are patients who will make a decision based upon the type of shrubbery outside the practice or the color of paint on the inside. This type of behavior is not typical.
And the fact of the matter stands. There are no current rankings for dental school. Period. So even if you have patients that pick schools based upon 'prestige', without any published standards, everything is more or less speculation and opinion. And online posts about school "A" vs. school "B" on a forums website means absolutely nothing in the great scheme of things.
A trained dentist with solid people skills and regarded results will generate business, regardless of the name on his/her degree.
Patients may ask where you went to school or where you trained. But no one is going to get up and leave the chair based on the answer. And only an ignoramus would be preemptively biased into believing that the job quality will be superior based upon a school name alone.