also on public roadways many times a bigger displacement engine is better because you have more torque to pull through corners, whereas the 600 sportbikes have to be wound up more. I realized this too with dirtbiking. A 125 2 stroke is still super fast but for the trail riding I was doing my ktm 450 4 stroke was a much better machine. It had the torque while rippin through the mud and up hills, plus the power band is wider, less finicky and requires much few gear changes.
also, dont rag on the chick for riding an enduro, in many cases enduros are awesome. You can get to remote areas and still hop on the slab to cover distance. A friend of mine went to a local track day and was beating many 600 sportbikes and duc's on a bmwr1150gs, which is a big enduro. Plus the guy had the stock tires and his adventure side cases mounted on the bike. In the straight he obviously lagged do to airdynamics (he kept it around 135 mph) but in the corners he made up for it.