Ride quality is a sum of many factors, prioritised differently from person to person.
I can think of one aspect of ride quality where hubs are suffering: transfer of vibrations from the road and various bumps. There are ways to absorb most of these before they reach your feet (flexi deck, shock pads, even gel shoe inserts), though they can have tradeoffs like less lastibility. But there is such a thing as good enough -for me hubs are good enough, for where I am riding them (mostly average quality pavement, mostly average quality roads). I cringe and slow down before I ride over some specific stretches of bad pavement on my commute every day, but they are a small part, the rest of the time I don’t feel/think about vibrations.
I would put minimal rolling drag as another factor of riding quality, and this is where hubs win, 100% of the time. For me that is very important -I like accelerating in bursts and feeling that my board rolls effortlessly between them.
Negative factors like heat dissipation don’t have the same weight to everyone universally. In some countries ambient temperature gets to 30-40C often, but where I live now it is between 0 and 15 something like 75% of the year -and rarely gets over 25.
Other things -like mentioned- maintainability. Motor mounts and belts can be a fucking pain in many ways. During the wet months where I live, dirt/mud/shit gets stuck in belt teeth and gears. I ride to work every day and am a lazy bastard, can’t be asked to clean stuff frequently. Clamp mounts also have a tendency to get loose or move laterally on the truck with time. With hubs I know I pretty much only have to worry about the bearing. If someone innovated finding a way to make the motor bearing easily replaceable, hubs would win this in every possible way -but they still win by far.
There is no inherent reason that hubs can’t support big wheels. I think the hubs of the Backfire Ranger show this beautifully. It is harder to make hubs transfer as much torque to the wheel at a 1:1 rotation rate, but it is doable.
There is never going to be one evolution, because there are enough people that prioritize things differently, and nothing comes without a disadvantage. But if there had to be one thing to exist and if esk8s reached wider adoption, I think the mass market would vote for hubs. Convenience is a big driver.
[PS] By the way the fact that Enertion failed doesn’t mean that R2 failed as a proof of what’s possible! It had a lot of QC issues as we know, but when judged by a best sample, I think it did prove you can have a hub-based board with that much torque perform reliably enough.