Grading knowledge workers based on ass-in-seat time is like grading programs based on lines of code. Which, as Bill Gates once famously said, is like grading aircrafts by weight. Time, lines, and weight aren't the goals of their respective domains, they're resources that are utilized to accomplish the goal. Judging solely by resource consumption penalizes efficiency.

I think part of the problem, at least in the States, is that we have this ideal of hard work and determination paying off, and lionizing work ethic above talent, skill, education, intelligence, etc. While it's certainly true that work ethic can overcome lack of any of the above, the idea that work == success is just as fallacious as the idea that, say, education == success. A little cleverness, plus a little laziness, can make often make the same amount of labor go a lot further, so judging just effort is missing a big part of the picture.