How exactly much is the IR reduction between the trough of the YF23 versus the 2D nozzle of the F-22, I keep hearing it's superior but by how much? Is it not possible to integrate new cooling solutions to the 2D nozzle to reduce the difference. A massive chunk of the rear of the aircraft has been removed, I wonder how much weight has been saved. The designers must have weighed the benefits of more control authority, versus how much IR reduction is lost versus how much additional weight is saved, et cetera.
Let's for one moment assume the NGAD is a delta canard with exhaust troughs, while the J-36 is a double diamond delta wing with 2D TVC. One design compromises frontal RCS in favor of superior IR, while the other design compromises IR, for superior frontal RCS. I don't want to start any arguments on Canards and RCS, this is an argument of overall design parameters, requirements, and cost benefit analysis.
You have a simple problem of tunnel visioning on one particular part of the aircraft, and not looking at the whole.