Stack ranking guarantees that the process isn't actually measuring if people are meeting expectations or not.

There are employee evaluation tools that try to measure if employees are meeting expectations.

The entire point of stack ranking is that it does not do this. The article is about a lead who resigned/got fired because the system wanted to penalise someone who was meetings expectations.

Because I doubt that the ranking system will be objective or even closely tied to any real measure of skill, performance, merit.

Who says they didn't meet expectations? As long as you define these expectations as "no other employee performs better than you".

There's nothing wrong with getting paid less if you don't meet performance expectations. I'm just impressed with the term they made up ("differentiated compensation") to try to make that sound nicer.