Using maida + bread flour to create AP flour substitute This is a follow-up to my earlier question about using bread flour instead of all-purpose flour in a banana bread recipe. The consensus was that using bread flour would yield a denser, chewier loaf, which could be undesirable (or perhaps desirable, depending on the eaters' preferences). 

Among the flours I have at hand is maida. As explained here and here, maida is a soft flour with around 7.5% gluten, similar to what is sold as cake flour in the US. My understanding from the Cooking for Engineers article linked from the latter question is that using such a low-gluten flour for this recipe would not be good:


  Cake flour is produced from soft wheat and is low in gluten content (8-10%). This flour is used for making delicate cakes. Baked goods made with cake flour has a tendency to crumble because of the low gluten content. 


This is the opposite danger to the one of using bread flour in the recipe: instead of being too dense and chewy, by using maida I risk making the bread too crumbly. 

Can I split the difference? Since maida is around 7.5% gluten and the bread flour I'm using (King Arthur) about 12.5% gluten, if I use 50-50 maida and bread flour, I would get a flour with (7.5 + 12.5) / 2 = 10% gluten. That is within the range of AP flour, which could be from 9% to 12% according to that Cooking for Engineers article. 

It seems to me that I could just combine maida and bread flour in equal proportions and use it, not just in this banana bread recipe, but in any recipe that calls for AP flour. Is this understanding sound? Or are there risks I'm not seeing in this approach? Are there specific properties other than the gluten/protein content of maida, bread flour, and AP flour that would cause the recipes to turn out badly?
Yes you can. 

Truth of the matter is... If you work in a pastry shop (which I did for a number of years), you use hard flour (high protein) for bread. You use cake or pastry flour for, you guessed it, cakes and pastries. If you really need an AP flour, it's fine to blend.

However, I was taught, and still to this day believe, that AP flour was created for home use only, back when people weren't super-sophisticated and didn't know (or want to know) the differences in flours. That was for a baker, who was supposed to have a real deep understanding.

I only have hard flour and Swans-Down Pastry Flour, and I use one of those for whatever I make. I would personally use the bread flour for my banana bread, and I would make it 'just mixed'. I am then not developing gluten from the protein. Also, protein is not gluten. Gluten is created by the mechanical mixing of the proteins.

Long story short, blending the two is fine. That's what AP flour is - a blend.