Good read, thanks.
I found this part bizarre
Higgins said the quarterbacks they worked with in Detroit loved the system, not only because of the simplicity and high success rate of the routes, but because of the security blanket installed with each play. No matter what, every play has a designed check-down option.
"On every route that’s devised, there’s always going to be a check-down," Higgins said. "We used to say, ‘as long as you can count to three you can be successful.’ If one isn’t there, look to two. If two isn’t there, reset your feet and make sure you find No. 3. There’s always going to be a nice check-down for you."
Doesn't every system have a designed check down on pass plays?