Here are some numbers. Assume a 65 kg rider (143 pounds). If he/she puts out 250 watts on a 170mm crank, this is 156 Newtons of force (35 pounds). Drop the cadence to 20 rpm and the resulting required force is 702 Newtons. This person weighs 637 newtons, BTW.
To take the steps thought experiment, assume that the steps are a 45 degree incline (pretty steep steps). This required 450 Newtons And the force required to basically go up a ladder at a constant velocity is body weight (637 newtons) and continual ladder climbing is probably tiring.
So this all kind of makes sense, whether or not maximum (as defined by strength) is a factor or not. I will say that now that I am doing a lot more low cadence pedaling as training, I get the sense that some work on a 45 degree incline sled would be helpful (could be wrong, of course).
dave
ps. I am assuming that I did the high school physics stuff right - 1966 was a long time ago.