It mentions tax rate laws, but those don't actually cover why Amazon effectively paid no taxes. I.e. massive investments in R&D, stock-based employee compensation, carry-forwards losses, and whatever else I may still be missing.

I don't think it can be considered fairly informative if it doesn't cover how we got to those values. From reading this article, one could still ask if a tax rate is at 21%, how does that mean a profitable company doesn't pay any taxes?