GPA is really important now that boards are PASS/FAIL. I went to a school that has grades and a GPA but they do not rank so then GPA is all a school would have to evaluate you unless theyt require the GRE for specialties soon.
Is it any easier to evaluate the top student in a class from one school to another? #20 from one school could conceivably outperform #1 from another school. That's one reason why I am a proponent of the pass/fail system.
IMO it would be much more effective to have a strong standardized testing system in place for specialization (or even job placement for that matter) - not simply multiple choice but something more advanced. Class rank tends to make students not want to work together and I think that's detrimental to the profession of dentistry as a whole.