You can try as hard to simulate a real emergency situation, but you will never be able to simulate people in fear of their life, and you probably do not want to, as we would probably see severely injured or even people killed during such tests.
Tests and simulations are great to compare different situations (i.e. evacuating a single aisle aircraft versus a widebody), but will never give you absolute results.
Current tests seem to deliver acceptable designs, aircraft which pass this test did proof in real accidents that evacuation of such aircraft works.
Seat density alone may not be the issue, on the contrary, if people leave their seat slower, they may block aisles and doors less, the overall number of people per minute and door may even increase.