We generated those statistics by getting lots of chunk plays on early downs... which can give a misleading conclusion.
We struggled when teams keyed on the run... and then we ran, a d that's WHY McD didn't run more in short yardage situations.
Zone-blocking teams with small backs don't run well there. ZB works best when defenses have to worry about the pass. This creates huge running lanes and it's why you hear coaches talking about 'linemen hitting their marks'.
In a straight power situation like 3rd and 2, your quick footed ZB linemen just don't perform very well, and neither do 190# backs.
To have our success on first and second down, we sacrifice power on third downs. There's just no way around this. Guys like Solomon Kindley SUCK at ZB, but succeed on 3rd and 2.
You can have one or the other... unless you can find a 210# back who still has enough speed to play on first down...
Which we just did.