The major advantage the 1hbh has is topspin potential. There is so much more room to swing and accelerate the racket. You're unencumbered by two hands, so the wrist is freer to supinate and get a snappy whip on the ball, like on the modern forehand. The modern forehand is an evolution of the forehand, like the modern 'windshield-wiper' 1hbh is an evolution of the 1hbh.
In today's spin-driven game, if someone with a very strong posterior shoulder and wrist extensors comes along with a 1hbh backhand like Nadal's forehand AND has a forehand like Nadal's forehand he would be a true nightmare to play on any high-bouncing surface. He could change the game. He could hook people off the court from either wing.
By contrast, I don't see the 2hbh evolving at all. It's the same old dependable but linear shot it always was. For players with a big spinny forehand and a 2hbh, once the ball is on their bh wing, their options are limited. They don't have access to the same topspin, therefore they don't have the same angles. They try to stay in the point until someone dumps their bh into the net, or go DTL to get a forehand.
The 2hbh is more dependable for rally consistency and ROS, but I don't see it evolving. I don't see anyone hitting crazy topspin with it - the 2nd hand will always limit that.
Basically the 2hbh is easier to pick up, but the 1hbh has the higher ceiling as far as potential. And has a greater potential to evolve into a crazy spin beast of a shot.