Bob:
I agree 100% with what (I think) your train of thought might be: we clamor for half-par holes as long as that "half-par" is "under-par."
The old courses not only had some very short "two-shot" holes (but likely not driveable), but also some brutally long one-shot holes (full drivers and brassies!). Many of the short par-fours simply became driveable over time. In the old days they were probably "nearly driveable" by the longest players (read Bobby Jones description of his "perfect" 66 at Sunningdale).
The Road Hole, on the other hand, has been a great half-par hole, regardless of whether the par was four or five!
Some might cite pace-of-play issues as rationale for abadoning the long one-shot hole. But don't "driveable" two shot holes and "reachable" three-shot holes create the same bottlenecks when most, if not all, of the field choose to go for it?