I'll simplify it for you, chef jrd - the most effective thing you can do as a pitcher is keep runners off the basepaths. If there's no one on base, other factors matter very little, if at all - ballpark, weather, pitch selection, defense, etc. What stat measures that best? WHIP. WHIP may not be an all encompassing super stat, but I will take the guy with the better WHIP 99% of the time. The only exception would be a guy with a huge sample size of starts that has shown, even when in trouble, he has a superhuman ability to strand runners.
Hunter kept runners of the basepaths better than Carlton did. That's the bottom line. Baseball 101 - unless you hit a ton of solo HRs, you can't score runs if no one's on base.