No, he explains that at the end. I can try to reformulate it. Imagine that you can find the orientation which gives you the maximum amount of power for a day, say E_max. If you have N panels, the total energy produced at the end of the day will be NE_max. If instead, you decide to put each panel in a specific direction, they will all produce energy E_i < E_max at the end of the day. So the total energy produce will be E_1 + E_2 + ... + E_N < NE_max.
that assumes the power of the sun absorbed by the panel has a linear relationship to the angle to the panel, or some similar assumption. It may not be the case
Trees don't rotate to face the sun. In order to have an optimal angle throughout the whole day, it would have to keep facing the sun, i.e. rotate.
I believe he may have missed this point.
As for the voltage measurement being the wrong metric -- agree.