In fact is +13 at 8 with proficiency. "Once on each of your turn". Don't apply even in AoO. 3d8+15 at third round (first bonus action to get soul knife, second for augmented weapon, you only start to use the off hand at third), half of encounter was gone, for 10 pp, you can do this 4 times day, for the cost of all your resources. Your bonus action is stuck with an attack every turn to get that damage, or you can burn even more pp for your nova, but forget the off hand attack in that turn. You didn't recover one single hp with mystical recovery, good luck trying to burn some hp for pp at lvl 10 with comsuptive power. In fact, good luck keeping alive being a frontliner with ac 17, and d8 of hp. You'll need to pick disciplines to bump your defense, harder for you who has 2 less. Your int is 16 instead of 20, easier to save than other mystics.
For 10 pp in a round I probably would prefer to use psychic crush for 7, or psychic grip for 6, or mind storm for 5, conjure two shadows for 3, or overwhelming attack for 7 (ready it to an ally turn, so he can get extra attack) or maybe with victory before combat to drop down half of the encounter before they can act.
Mystic have great versatility, but not good at will damage. Soul knife looks like he is trying to swim against the tide, burning all they versatility to get an "ok" damage compared with standard martial classes. The idea of make him a dual weapon fighter with 63739282764 another uses for bonus action is really bad idea.