Macronutrients and cooking temperature of beans?
This is going to be a bit of a Zen answer (as usual for me).

I would venture that it doesn't matter. Normally, when you're making a bean stew or a chili bean casserole, you won't be discarding the liquid anyway. When you're eating the final dish, it doesn't matter to you if the protein is in the bean or the liquid, as you're eating them both.

It has, however, been my experience with white beans and chickpeas, that if you cook them more slowly, the water gets gloopier (higher viscosity), which means that proteins have moved from bean to water.