In 2007 at “Beyond the Boxscore” I posted an article called
"Bert Blyleven: As Dominating as Sandy Koufax
Over a 5 year stretch, both of them were 22 runs better than the 2nd best pitcher."
That was using a stat called RSAA or Runs saved against average. "It's the amount of runs that a pitcher saved vs. what an average pitcher would have allowed," as explained in the Lee Sinins Complete Baseball Encyclopedia. It is also adjusted for park effects.
I then went on to show that Blyleven was comparable to Koufax in strikeout-to-walk ratio and HRs allowed when park effects were factored in. Blyleven may have been a dominant pitcher during that time and no one really noticed.