This is an interesting altitude-control scheme. When I think about this problem, I consider a method that involves a flexible helium container (in the simplest form, a helium balloon) and a control system that involves pumping helium out of the balloon into a high-pressure tank to descend, and releasing it from the tank to the balloon to rise. It's a variation on the submarine buoyancy method, which also requires power to run pumps.
The advantage is that the method doesn't just throw away the helium, it recycles it, but the recycling activity require a lot of power. And it's way complicated compared to your method.
The advantage is that the method doesn't just throw away the helium, it recycles it, but the recycling activity require a lot of power. And it's way complicated compared to your method.