You have your own bias, which comes through loud and clear. Simply repeating something and screaming at people doesn't make your opinions into facts.
I've used a 6' RC and a 6' flail mower on the same property, for the same tasks, for roughly 4 1/2 years each. The flail mower did all the mowing I wanted for tall grass, tall weeds, and woody brush up to about 1" diameter. It did not require more HP than the RC in my actual use. There was no difference in forward speed in my actual use, because ground roughness (and the areas were smooth by farm standards) limited my forward speed before any mowing issue did.
For my use on that farm, what did the RC do better for me? Nothing.
What did the flail do better for me? Several things:
-it cuts along a line and it doesn't stick out as much, so while mowing inside of fenced pastures I can turn closer to a corner without the mower swinging wide and hitting the fence.
-likewise I can back into corners to get the last few feet, and get it completely, because it cuts a line instead of a circular arc.
-it mulches the cut material, which the RC doesn't do. Even with 3' tall grass/weeds I didn't have dead or matted vegetation underneath, the cuttings fell to the soil within a few days and decomposed.
-it doesn't spit rocks any great distance. Yeah, it can still throw a rock 10-20 yards (which happened one single time over 4 1/2 years), but I saw my RC throw a baseball sized rock about 75 yards. I always kept people away from mowing, but a 75 yard danger distance means it's a hazard to mow roughly half that property (house and barn near the center in both axes). A rock that size thrown by the RC will not only go through glass but will break vinyl siding and severely dent steel siding. It may not happen often, but it's a greater danger than with the flail.