Big D,
The recoil formula be it on paper or calculator uses muzzle velocity as a factor and NOT pressure. Peak pressure is certainly not a factor. As you deduced, the total units of pressure over the time from primer ignition to wad leaving the barrel (and maybe a smiggon or time after that?) is what does the work of accelerating the wad and shot to muzzle velocity.
I agree with your theory of slower burning powder creating less felt recoil but there have been tests conducted that resulted in the opposite! Go figure...
