The friction drive system is an area where I actually have some experience. There are many facets that are the opposite of a (hubmotor) driving the core of a wheel.
With a direct drive hubmotor, best torque and efficiency is a large diameter motor in a small diameter wheel.
With friction drive, a small diameter motor works fine, and best hill-climbing torque is on a large diameter wheel (Visualize the Friction Drive At 12:00 On the wheel, and the wheel diameter provides leverage.
I have been able to get consistent results up to 1,000W, using 36V, and it remains a useful option if products from China become restricted due to a trade war.
As Amberwolf said, the road-speed of the bike is the same as the friction roller speed. Sounds odd, But It's true.