Because of the order of activation, one thing is clear: a maximum test will activate the most muscle fibres simultaneously.
Does this mean, that only one repetition with maximum strength is the best way to build up muscle mass?
Logical answer: NO!
You never use all your muscle fibres simultaneously. If you would, you would be unable to move after a maximum test.

In a single repetition however, you learn your body to activate as much muscle fibres as possible simultaneously!

A karateka who wants to break a brick with the side of his hand, needs no gigantic muscles. He needs 100% concentration to bring his hand to a maximum speed.
This requires a special training of the internal muscle coordination.

Maybe this is nothing new for you. But this is one more important piece of puzzle to understand the overall picture.