You can also generate electricity using high torque and low speed without a gearbox, if you just put more windings in your generator. I believe some offshore rigs use a setup like this, because fewer moving parts means less maintenance required.
Re: Dip in the blade - maybe for tip vortices but I don’t know how. I am a glider pilot and have some understanding of the aerodynamics of wings. The picture of the glider in the link you posted shows winglets and the non-linear leading edge of the wing but the shape that I am seeing isn’t either of those things. Maybe l’ll ask this question on the glider forum I frequent. There are a lot of aerodynamic experts on there.