That makes no sense. You might be able to say that they have less power for a given cylinder size. You might say that a "gallon" of compressed natural gas has less energy than a gallon of gasoline. But you can run locomotives on natural gas, so power isn't a problem.
My thoughts as well.
It would apply more to converting a gasoline car into a CNG. It is not going to run the same on methane as gasoline.
Just heard a podcast on this very thing -
NG, even compressed, is “fluffier” than vaporized gasoline.
It has about 80% of the energy per volume entering the combustion chamber.
But, folks, at 75 cents per gasoline gallon equivalent, gimme a break! I’ll take the “gotta push my foot down 20% more” problem.
On topic, though - since NG will work, and electric cars will not, look for the left to support electrics over NG.
If the engine is designed, built and tuned from the ground up for natural gas, they can be pretty good. Everything I’ve seen is a converted gasoline engine.