and we are required to meet 20.7.1b every day
Your post appears to imply that your aircraft only looks at established gradients rather than the full Part 25 thing . two very different animals. I would still be interested in having a look at the POH FMS.
And face it, in an accident scenario, the cert standards et al, can go jump, as long as the perf manual gave me a gradient and it met what I needed
Well, no.
The certification documentation, being the basis for the TC, is the source material for the operational numbers. Alternatively, the STC workup may have done the donkey work again for the new requirements.
I guess so long as the pilot is compliant with the Ops Manual, and the operator has taken advantage of CAR(1988) 139(3) - ie the pilot has never seen the AFM, he/she probably is going to have a reasonable time of things.
However, if the ops data doesn't fit the AFM then others may have their delicates out in the cold breezes.