PennKev, You are correct but medium action rods generally do not perform well at distances much greater than 50 feet or so - they are designed to load at shorter distances. When it comes to long range cannons, you don't see rod companies designing medium action rods, they design fast action or even ultra fast action.
So while it is true that the design of the rod dictates performance, a medium action design is best suited for short range casting - not long distance - whereas as certain fast action rods are definitely as good as medium action rods at short ranges plus with the added benefit that they can toss 80 feet of line with ease. And some fast action rods are better at shorter ranges that others while some are better at longer distances.
The whole statement by Jeep was misleading by making it sound like if you are a good caster you can take any rod and get it to perform equally well under all conditions. I, not an expert caster, and many true expert casters do not subscribe to that theory.
Here are two excerpts from the Yellowstone Anglers 2011 5wt Shootout.
Sage TCX
Performance at 25 feet – 12 points out of 20
This rod is far too stiff for a #5 line! Almost no feel whatsoever made judging the distance and making accurate casts very difficult. Accuracy was terrible. I switched over to a #6 GPX line and then it was much better, not great, but better at both 25 and 45 feet.
Performance at 70 feet – 19 points out of 20
Finally, the power of this rod makes it come alive with a lot of line in the air. Now I can cast nice tight, controlled loops and get good accuracy. Still not in the same league with the Zenith or NRX with a #5 line at this distance.
Winston BiiiX
Performance at 25 feet: 20 points out of 20
In big letters my notes read: Light and Just Right! That just about sums it up. This rod has a wonderful feel in my hand, loads perfectly, and with its very light swing weight it is a delightful rod for fishing at shorter distances. With better balance and the slightly stiffer tip, it was far more accurate than the older BIIx. If you love fishing dry flies at short to medium distances like I do, you are going to love this rod!
Performance at 70 feet: 18 points out of 20
The overall power, which loaded the rod perfectly at shorter distances is not quite enough to match the more powerful NRX, Z-Axis and the Hardy Zenith, all of which threw tighter loops and posted a more solid performance at long distance. The BIIIx required a harder double haul than the other rods at this distance and the accuracy suffered somewhat. In a direct comparison to the NRX, Z-Axis, and Zenith there was no question that they were all better at long range.