"Some manufacturers and inventors have made claims of exceeding the limit by using nozzles and other wind diversion devices, usually by misrepresenting the Betz limit and calculating only the rotor area and not the total input of air contributing to the wind energy extracted from the system."
Betz law works for a free flow. Turbine you showed does not work in free flow to achieve the efficiency you showed, it works with a large vessel, that stops the water from just flowing all around the turbine. By Betz law you need to account all of that structure, not just thr rotor. Then efficiency will be comparable to what betz law suggests.
Why dont we build such turbines in free flow? Because they only work with a large concrete structure around it. That is costly. When alone, 'efficiency' will drop to well below of what Betz law suggests.
Why is it so? Because as you create larger pressure drop, more fluid goes around, and you loose power in a free flow. In restricted flow this is not an issue, flow doesnt get around.
We dont use such turbines in ocean free flow either. We use turbines that are very similar to wind turbines. They are optimal for a free flow, where fluid has an option to go around.
Also specifically your design: fluid will also just go through the intake horizontally, because flow is from one side, nothing will push it vertically, so it will not work in a whole new way as well.
P.S. it has nothing to do with fluid being gas or liquid. Its just that rivers of water are more common than rivers of air.