>I'm not sure why they have a he-man scale going up to 11

There's a big difference between air resistance and magnetic resistance machines. Air resistance scales with the square of velocity, the same as real rowing, while magnetic resistance is linear. On an air resistance machine you can get a good workout by keeping the difficulty setting realistically low and rowing faster, but on a magnetic resistance machine you'll end up going so fast it becomes difficult to maintain good technique. The higher difficulty settings are more useful on a magnetic resistance machine.

It's funny you just mentioned this because we just learned a few weeks ago in physiology about Henneman's Size Principle: that the somatic nervous system recruits smaller skeletal muscle motor units (1) followed by larger motor units as the amount of force needed increases.

That would make resistance training by rowing in water better fit than some magnetic resistance machine based on what you described. Air also has same property like any other fluid, your average big body of water has enough viscosity for this property to matter at speeds we don't need cybernetics and Tommy John's surgery to survive.

(1) A motor unit is just all the muscle fibers controlled by 1 motor neuron. With this single source of signals, all those muscle fibers respond the same way.