Nothing wrong with using a bark mix. IF you remember to REPOT every 2 to 4 years. Bark is no good if you want to go 5 to 10 years between repotting. If you repot the ones in a bark mix, they should pick up growth and maintain it for a couple years, then time to repot again. Bark is dynamic, it changes its structure over time. This can be good, especially if you are growing trees that need acidic conditions, as bark breaking down becomes more acidic. Not so good when you don't need the acidic conditions. Also, 50% bark is pretty heavy. For my pines I usually keep bark around 10 %, and for spruces and hemlock I keep bark around 25% component. Blueberries are the ones that get the 50% bark & 50 % peat moss.
For a bark mix use a HIGH NITROGEN fertilizer. 20-20-20 is NOT high nitrogen, in fact it is poorly balanced, or not balanced at all in terms of what the trees actually use. I use a 13-1-4 fertilizer with good results, it has a long list is micro-nutrients too. PM me if you want some, I occasionally package and sell what I use.
Pumice is great. If it is working for you, keep using it. No need to change a good thing.
DE- I would never use any component at 100% of a mix. Pumice is the only exception I make. Everything else I use as a mix. DE is great, but I have never gone over 25% DE as a mix component. When I tried 100% DE, the results were not good, at least in my conditions.
Granite, Decomposed Granite, and crushed Quartzite - None of the particles hold water internally. THeir water holding is just the water film on the outside of the particles. A granite mix will be a dry mix. You are in Arizona in not the place I would ever tempt fate by using a dry mix, unless I were raising cactus. Also, granite is heavy. A 5 gallon nursery pot could weight 75 pounds. I'm too old to be throwing around that kind of weight. As a component it is good for "drying out" a mix. I have used it as a 25% component in one of my earlier pine mixes, but I have since gone to pumice, just because I got tired of straining my back moving trees around.