I think the phrase here "pitching backwards" may mean different things to different folks. When I hear that phrase, it simply means starting off "soft" be it change up, CB, etc....that is typically employed with a very aggressive swinging team, or middle lineup guys....rarely to bottom of order guys. It does NOT preclude throwing fast balls, and should not imply throwing more off speed than FB.
Change ups are VERY difficult to learn, everyone I talk to claims a change up as part of their arsenal. VERY few of them have I seen throw an actual "good" legitimate change up. Most youth (including HS) pitchers that throw a change up, are actually throwing a "bad fastball". A change up is an actual pitch (not a slow FB), and if thrown correctly (with fastball arm speed, and same arm slot), then it can be a devastating pitch....I just don't see them thrown well very often.....and is a very hard pitch to master.
Also, I am not sure about the success of throwing off speed pitches for strikes. I teach to get ahead locating FB, and get batters to swing at balls for outs / strikeouts. Yes, there are times you can get by throwing a "get me over CB, or maybe even change up" but those are rare. Typically at the higher levels, you see the off speed pitches thrown either perfect (barely in the strike zone), or more likely outside of the strike zone. With a change up, the pitch should be "perfect or in the dirt"...above that zone, they typically get hit, and don't come back.
Look at this past WS where Uehara was virtually unhittable...you saw many swing and misses, however virtually none of the change ups were in the zone.
Pitching backwards is a way of saying messing up a hitters timing / expectations...not strict diet of off speed. A well located 2 seam, 4 seam, and good breaking pitch is all that is needed at the HS level to be successful. And most important is that all pitches have the same arm speed, and release window...that is one of the most important things I don't see taught, and one of the biggest common denominators you see in elite pitching at the highest levels.
I hear a lot of folks talking about a 12-6 CB....tough to throw if you are not an over the top arm slot pitcher. How does a high 3/4, or low 3/4 arm slot throw a 12-6 CB without changing his arm slot? Once he changes his arm slot, guess what happens at the higher levels...the arm slot change tips off the hitter, and the ball gets crushed. The things required to have a successful CB IMO, is fastball arm speed, same release window as the FB, and good late break with depth to it....you can get that without a 12-6....in fact since most MLB pitchers are not over the top, you don't see many 12-6. Kershaw likely has the best wipeout CB in the bigs right now, and it comes out with FB arms speed, but looks like a soap bubble going to the plate (up to 20MPH) slower than his FB...exceptional. Others throw it hard, with a late (the bottom fell out) break.
my .02 cents