Well actually since produced power is proportional to glide ratio (of kite and tether) and lift coefficient (P \propto C_L G_e^2), the magnus based wing is a bit difficult to compare, because it has way smaller G_e and way larger C_L compared to a foil wing. But I believe that in sum the magnus wing is not bad or perhaps even very good relative to it’s size.
While C_L will always be very good for the magnus wing and always poor in comparison for the foil wing, the number G_e gets worse with longer tether. I am in the opinion that tether drag is of highest importance for single kite AWE energy. An efficient wing is not as efficient combined with a long tether. An inefficient magnus wing is not much more inefficient comparing with and without tether.
The end result is that the magnus based wing could beat the efficient wing hands down on longer tethers. And longer tethers of course is the key to high altitude AWE, which in turn is one of the bigger carrots we are chasing here. (The argument being exactly the same as for a lightweight foil kite with larger surface area and lower G_e compared to rigid wings)
Looking briefly at lift-to-drag curves, it also seems that magnus based wings have their highest G_e where C_L is at its highest (the curve pointing up towards left in the chart). This means that the point where these are both at their maximum coincides with the working point for AWE. This is not true for most wings, and in particular it is a “well known truth” that G_e for many foil kites is worse at high C_L (a truth I have heard stated several times but cannot document myself).
Last, the magnus wing is quite easy to build strong and lightweight, as it could be an inflated cylinder. The cylinder might even be less dangerous in the event of a crash compared to a carbon plane. I would guess for example that even a big magnus wing would not penetrate a house wall or enter a car. Because it is so volumous it cannot even attain very high speeds free falling…
Compared to large soft kites, the magnus kites are a lot smaller and easier to handle due to their stiffer construction.
There are of course some bad points about such wings also, but being the most optimistic person here now (?) I don’t think it necessary to go there…