"If Nick Zito could get BIRDSTONE to win the Belmont at a 1 1/2 off of a 5 week layoff...."

I agree.

Frankel won the Belmont off 5 weeks also.

There is nothing intuitive to me about why 5 weeks would be much tougher than 4. There was nothing in any statistics I have ever compiled or seen that suggests that 5 weeks would be very difficult for a competent trainer (assuming it was intentional and not because of an interrupted training schedule).