Whether a stiffer frame is of any benefit to us has been debated for years. Most of us, especially those of us over 50, would benefit from a more forgiving frame, especially on rough roads.
I think the whole stiffer is better thing is over rated. Fit and comfort are the most important.
The racers, the top pros at least, ride what the sponsor gives them.
Whether one design is stiffer than another just by the position of the top tube on the seat tube is questionable, as well. The absolute stiffest, most bone jarring, teeth rattling bike I have ridden is my Tesch s-22. This is a steel, conventional, 64 cm frame with short wheelbase and steep angles. Why anyone would want anything stiffer than that bike is beyond me. It makes my Cannondale feel like a Cadillac. The Cannondale CAAD5 however, makes the Gunnar feel soft and cushy, but the Gunnar has a sloping top tube. I once had a Landshark made from Tange Prestige tubing in size 63cm conventional. This was the softest riding road bike I've had and was so whippy, I knew it would break if I kept riding it. Surprisingly, I could climb on it as well as I have on anything else, even though when I stood up on it the bottom bracket would sway from side to side as if it was broken.
The racers, the top pros at least, ride what the sponsor gives them.