Having ridden a pretty powerful sport bike/sport-tourer (1200 Bandit), I can say that I find dual sports to be more practical and even more fun to ride. I will admit I have never really understood the supermoto thing, though I have given it thought since I tend to respect every motorcycle for the type of experience it offers.
When im on my bandit (cammed, header/exhaust, timing advance, jetted, 1 tooth down front sprocket), I have "power" through the throttle grip- sheer brutal acceleration and torque (Bandits have a lot of midrange) that allows me to pull out in the smallest of gaps, completely OWN any vehicle I see, and of course to FEEL that rush as the speedo climbs.. too fast. But then, it feels limiting to me as well. You can only use that power so much. You can only ride on the roads available. You can only push in a corner so much because you have to watch out for asshats pulling out in front of you, cats, deer, cops, oil on the street, dirt, gravel, etc. You are in a prison of sorts. With a dual sport, that "power" is that there is no road. That big 21" inch front (and accompanying knobbies) makes curbs, stairs, parking lots, ditches, yards, etc feel like part of the road- just made of different materials.
Where im going with this: if I had to guess why supermotos arent super popular, I would say its because they take on all the limitations of a streetbike (except they do have more suspension travel) where they are fairly limited to street (bar exceptional skill) while having few of the usable benefits of a streetbike- namely power (but also storage, comfort, etc). They dont have the power of a sportbike (most of us love power), the comfort of a crusier, or the go-anywhere of a dual sport. Supermoto on the track makes sense to me as there arent so many variables and I can see why it would be fun; loooots of lean angle, low weight, and the speeds are slow enough relative to some literbike that you can enjoy it without being so close to death.
Not trying to say any of you sumos are wrong (ride what makes you smile)- just explaining it from the perspective of a guy who loves all bikes but doesnt really find the supermoto gig appealing