For what it's worth, the Reds' starters' aERA (Fangraphs' adjusted ERA or ERA-, which is like B-Ref's ERA+) is 86. That's second behind only the Tigers' 83. It's league and park adjusted.
Looking back 50 years, only a total of 67 teams have better aERAs in that time. So it's not anywhere near in a class by itself, but it's a really good staff. Looking at the numbers, the 2011 Phillies' starters are by far the best group. The Braves' staffs of the 90s were close competitors a couple of times, but the Phillies' numbers were astounding.