how is the prep time any different between the two? it's just a matter of rotating your body.
moving on from pure power, the one hander has the benefit of more disguise. one can move quickly from slice to topspin/flat during the turn. if you are a two hander, it's pretty obvious when you'll go for a slice.
Disclaimer: I'm NOT a coach...
Real tennis: https://www.youtube.com/watch?v=yDqnkLJ9BtM