playing double won't earn you as much training points as playing single.
You don't earn any training point if you already have 50 of them, when you have a double victory.
But you'll earn 1 point in forehand volley, backhand volley, and smash...
You'll earn 25 points for a loss in double, same as a loss in single.
So yup, playing double will help you to achieve an higher overall percentage in skills, but not 2 times more.
But you can try and let me know how high u can get..!