The best efficiency of a 100% impulse turbine using a liquid as the driving fluid is 95% while the gas equivalent is only 80%.
The nozzle efficiency for a liquid isn't much below 95% so the buckets on the pelton wheel must be pretty close to 100% efficient at converting the linear kinetic energy of the fluid stream to rotational shaft work.
A reasonable efficiency for a gas nozzle is about 93% so 13% of energy is lost spinning the lavel turbine.
I'm guessing windage is one to three orders of magnitude more important in the gas turbine than the liquid turbine, partly because the speed and U^2 term causing drag is much higher and partly because of the differences in densities of the working fluids with the surrounding fluid which is a gas. You couldn't get 95% efficiency from a pelton wheel submerged in water.
Most photos and drawings show only have one or two nozzles for the pelton wheel while the lavel turbine has "high admittance" -- the full circle of nozzles in all gast turbines.
I've seen patents for stationary power plants where waste industrial gas under pressure displaces water out of a vessel to drive a water turbine. Two vessels are used in tandem for continuous operation. Floating ceramic balls insulate the liquid from hot gases.
Most industrial gas turbines are aeroderivatives which don't use the lavel turbine.
Bret Cahill