You can do the same thing with compressed gas as well, or really anything. Gas and fluid do make the most sense in terms of directly driving generator turbines though. The only issue with gas is thst you have to deal with thermal effects from expansion and compression.

Tidal generation using dams is a very bad idea. You're taking energy from and releasing energy to the system at times when it's most detrimental to the inertia of the system. Basically you're stealing inertia from the rotation if the earth, which would be ok, except you're amplifying the effects because of timing. You can think of it like swinging in a swing. The way you build up a huge amount of momentum is by shifting your weight at the peaks and troughs of the arc.