The question was: how do gorillas get so muscular on a mostly plant based diet?

The correct answer is: they eat a shitload of protein that is present in the plants they eat, by consuming 20-30% of their calories from protein and eating 25-40kg of food per day.

Your answer included factually incorrect claims about how gorillas can synthesize any amino acid so that the concept of nutritionally essential amino acids don't apply to them.