I love almost all of this--I'm going to get that book, as I've been looking for a compact explanation of the development of the field of thought; and I think you do a great job dissecting the hype away from the reality, and the label away from the actions that need to be taken and the injustices that need to be corrected. Great stuff!
However, as a point of accuracy, "To receive an A, you still need to pull between 90 and 100. What their new rule did was change from a 100-point grading system to a 50-point system. A student will no longer receive a demoralizing zero. An F will be 50 to 59." cannot be anything but lowering standards using any simple (linear) grading scheme. It's just mathematically impossible.
Here are three ways they could try to make it work out that way (and fail).
1. They could start everyone at 50 points, and points would go up from there. Then getting all but the top 20% of points would give you an A, whereas before it was 10%. Lowering standards at the top.
2. They could score and grade as before, except that 0+0+0+0+0 = 50. Now you can't tell the difference between someone who put in some inadequate effort and someone who did nothing. Lowering standards at the bottom.
3. They could score and grade as before, except the range 0-60 is compressed into 50-60, by dividing by 6 and adding 50. Firstly, this is unlikely to fool anyone (except, I guess, some folks who are getting 0 on their math scores). Secondly, it's still lowering standards at the bottom because it says that the difference between 52 (12 raw score) and 58 (48 raw score) is the same as the difference between 82 (82 raw score) and 88 (88 raw score). So you still are lowering standards at the bottom.
Compressing the grading range is unavoidably lowering standards somewhere. Isn't that literally the point? To avoid "the demoralizing zero"? If you so bad at something that it counts for nothing at all, and you're not acknowledging that this is how bad it is, that's lowering standards by definition.
The rest, as I said, is great.