The back brake provides not more than 15% the total braking power. The front brakes are by far the more used and the more effective.
On a motorcycle, the weight shift is even more predominate than on a car. This is one reason that the front brake predominates. For a clue - look at the relative braking surface between front and back on a modern bike. It will be obvious that the manufacturers think the front is more important!!
As to which to apply first - I do the front brake almost exclusively, except for two situations: (1) when there is danger of locking up such as on loose gravel or dirt on the road (you lock the front wheel, you go down!) and (2) when maximum braking power is required - then both should be applied simultaneously.
I guess things have changed.....