You have a good point about power being a consideration, but this point doesn't necessarily follow. If the plant is cheap enough more scale can overcome the lesser power output.
Growing corn is cheap, but there isn't enough arable land on the planet to replace gasoline with E85. How much hydrogen is required to replace 1 gallon of gasoline for an equivalent amount of useful travel in an average car? How much gasoline do we consume as a nation daily? How big does this new hydrogen plant have to be to replace 10% of our daily use? How long will it take to install adequate infrastructure all over the U.S. to make travel in a hydrogen car even possible?