Your ignorance on this subject is quite annoying.
Go watch footage of Federer’s 1-handed return of serve or footage of when he takes the ball early. The racquet starts off low-mid thigh and ends shoulder height. No backswing required.
The only time you need to take a backswing is when you have plenty of time to set up. Even then, it is a restricted backhand.
Now, from my own personal experience (I have used both 2 and 1-handed extensively in USTA Junior’s and I was pretty darn good) the 2-handed limits creativity and is pretty darn predictable. It’s reach is also quite limited so it takes more energy to use a 2-handed because one must take 1+ more steps to reach a ball than a 1-handed.
A 1-handed, on the other hand, has great reach, very unpredictable (easy to conceal a slice or dropshot by making it look like your regular stroke) and can create angles that the 2 can’t hope to match.
There is more to the stroke than just how much you move the racquet head ya know.
The ONLY weakness (and it’s a big one) of the 1-hander is the high (above shoulder height) backhand shot. That sucker is HARD. Other than that, the 1-hander is better in every way. The 2-hander is easier to learn and requires less athletic ability to become consistent. That is why it is prevalent.
But what do I know? I’ve only played tennis for 20 years.
Edit:
A second weakness (I suppose) would be that the 1-hander requries near perfect timing every shot or you’ll be shanking the ball into the stands.
In fact if Venus Williams were healthy, you could set up a match between her and Federer, best two of three sets, nobody hits a forehand and no serving, put the ball in play with a machine, and Federer would lose that one as well, that would be an efficient shot versus an inefficient shot.