I'm not saying the stat is without use entirely. If you get a large enough sample size, the metric's arbitrary nature will sort itself out over the long run, as many stats do. But in a world where we have hundreds of metrics available to you, why use something that is so obviously flawed over the short term and unnecessarily boxes itself in? Any time you reduce the number of inputs in a metric and combine it with a shorter period of sample time, the more flawed your stat. Quality Starts takes IP and Earned Runs, two stats that are broken down into the many pieces every start (usually 4-9 for IP, 1-infinity for ER), and reduces them to one boolean output in total (each input doesn't even get its own output, as both inputs must be met for a "yes" output). So, over the course of, let's say a month, you have reduced ~35 IP and ~17 ER (in other words, many input/output figures) into 5-6 boolean "yes" or "no" outputs. Instead of getting a more nuanced look at a guy's pitching (say, 36.2 IP over 5 starts with 14 ER allowed), you get an output of "4". And that's not even bringing up the completely arbitrary nature of "6 IP, 3ER". In my experience, QS is often used by people who want to prove a point with a single number, except every other stat says something differently so they can't use any conventional metrics to illustrate their point. It's way too easy to use the QS to cherry-pick whatever information you want to tell because it's so incomplete and arbitrary.