So once again they can't actually find discrimination and resort to using disparate impact as "evidence".
Once again, you miss the point. Nowhere in the OP did I claim discrimination. The algorithms (made via explicit choices by people) create a disparate outcome. No one forces the IRS to make these decisions to come to this outcome.
This results suggests there is something wrong. Most people when confronted with something that appears wrong and unfair wish to change the process. So instead of misconstruing the OP content and making excuses for this unfair outcome that increases the level of distrust of the IRS which may possibly reduce the level of voluntary compliance, why not ask what can be done to improve the situation?
BTW, now that the IRS knows about this, and if it follows your implicit advice of "tough nuggies", then it becomes discrimination via inaction.