I think what you want to know is what percentage of starts is worse than 6/3. Finding out what percentage is 6/3 or better doesn't really tell you anything about the 6/3. Anyway, I believe something like 51% of starts fail to qualify as "quality". The problem with that, however, is a start that goes 8/4 or 9/4 isn't considered quality, while 6/3 is. Likewise, 5/2 isn't quality either. Anyway, I'd say it's safe to say that about half of all starts, that includes everybody who starts a game, whether it's a reliever spot starting, a guy coming back from injury, or an ace, are better than the lowest possible "quality" outcome. And that doesn't really qualify as quality in my opinion.