The evac criteria seem quite reasonable. The Air France A340 evac at Toronto after a major overrun and consequent fire, with all OK showed that it was quite an appropraite set of requirements.
The Japanese 747s with about 540 seats, with only a small business class, rest all-economy seated, were fine, and still inside the evac requirements with a margin. That margin is your assurance.
A commercial failure was the original 737-900. This looked at the 737-800, evac limit of 189 seats, noted that most mainstream mixed FY class operators in fact only had about 150 seats in it, and did a stretch which had about 180 mixed class and still met the evac limits without changing the exits, but squeezing that margin. Such an aircraft was not saleable (or re-leaseable) to the LCCs of this world, but theoretically would suit mainstream carriers. It was a sales flop (with good reason). The 737-900ER re-engineered the exits with larger doors etc which gave a standard evac limit, and has been notably more successful.