Well, that's one way. Getting first downs by foot or by arm both keep drives going, and get in the end zone. A 5 yard completion is not inherently superior to a 5 yard run. Throwing for 300 yards and only getting 1 TD out of it isn't exactly superior either.
As an extreme example of offensive scoring efficiency compared to yardage was the Patriots 8th ranked offense which scored more than 75 points more than the top ranked offense. The goal isn't actually to make more completions, or to accumulate more yards...but rather to score more points.
A QBs job is completing passes. If he does that everything else will follow. Tebow doesn’t, not much follows.