The reason why they are so large is because the power harvested by a windmill goes up with the square of the rotor diameter
Doesn't the Makani wings get around this issue by equivalent to a turbine with a massive wingspan and a wingtip that generates power, but without the rest of the structure?
The outer third of the blades account for roughly 60% of the total power generated by a windmill, the 'massive wingspan' would have to be normal to the direction of the wind, in order to say more about what Makani does or does not do there would have to be a lot more design data available than there is now.
Windmills with 'just the tips' have been proposed and constructed, there are some good reasons to include the blade all the way to the root. Part of that is to stem vibration, also to help with rotor start-up and low wind conditions.
It is normal to the wind direction, that's clear on the site. From the way you're talking it doesn't sound like you bothered to even look at what they're doing.
Doesn't the Makani wings get around this issue by equivalent to a turbine with a massive wingspan and a wingtip that generates power, but without the rest of the structure?