Dabiri’s purpose is the optimization of a whole wind-farm, not VAWT as such even though he experimented them. Now, he studies HAWT by “pointing turbines slightly away from oncoming wind”.
Maximizing Betz leads to maximizing the power/space use ratio. A “truly workable system” producing 1 MW by taking 3 km² land will never be bought. So maximizing Betz is a part of a “truly workable system”.