You may seriously want to consider going ahead and getting a SWG. With that, in phoenix, your CYA should be 70, maybe 80, so maybe you would not need to drain the whole pool.
One thing that you might want to try, and the accuracy when you do this is not perfect, but make up a gallon of test water. Take 50% from your pool, and 50% from your tap. Mix them together. Then perform a CYA test on the mixed water. Your result will actually be 2x due to the dilution. Now you might ask, why? So if with this dilution, your CYA tests about 70, then this tell you that your actually CYA is 140. You can drain half the water out, refill, and get back to a real CYA of 70, which is perfect if you have a SWG. But when you do this, if your CYA tests at 100 diluted, that means your CYA is 200+ without the dilution, and at that point, complete drain and refill is probably the best way to go.
Unfortunately your story of your PB and "Pool School" is way too common of a story. It is a necessary evil that the PBs have to do, but dont want to do. They look at it as a half day of work lost, generating no income. PBs work their butt off building pools, they dont necessarily learn about new technologies, advanced techniques, etc. They learn something to start with, its good enough to get teh job done, and never try to get better. Now of course, this is a over generalized stereotype, but it is way to common to hear the exact story.