skiesfull, I think that you've nailed the source of the disagreement between the parties involved here, that is, a disagreement between the "theoreticians and the practitioners". I have had a fortunate career in having simultaneously lived in both the theoretical and the practical world, and I remain confident in my statement that THE NUMBERS WORK, USE THEM!
This has been proven to me again and again in certification test flying, Performance Engineering to "put the numbers together", and then the sometimes heart stopping moment of taking the performance data that I've produced into a real aircraft with real live people in it, and proving that it works - IT DOES. The non-stressful bit is the other part of my regular job of line flying, non-stressful because I'm comfortable that the unmeddled with figures work.
It worries me that in this area, there is very small latitude for error or adjustment in the OEI situation, and any fiddling with the figures may lead to disaster.
Regards,
Old Smokey