I think you are over thinking and and mis-interpreting the point of the "theory of mashing" article. That table regarding mash temp and attenuation is only specific to the wort tested. It's meant as a demonstration of how increasing temps may make a less fermentable wort.
Fermentability of a wort is based on much more than temperature of the mash. The composition of the grist can have a much bigger effect than temp alone. Manipulating temps is a tool for overcoming the limitations of the grist. Consider the differences between three grists: 100% 2-row, 50% corn- 50% 2-row, 50%corn 50% Munich. In each case the total diastatic power of the grist is different. If you mashed each one at the same temp you'd likely get three different attenuations. There is no way to calculate the fermentability of your wort. It can only be tested.
In general, you are correct however in assuming that which ever factor is the least attenuative that will drive your attenuation. A 100% fermentable sugar solution will only attenuate to the level that the yeast can tolerate the alcohol or lack of nutrients. Where as if you make a wort that contains 30% non fermentables; a yeast that can go to 80% attenuation will stop at 70% attenuation because there is nothing left to ferment.