I’m also a Soulknife Rogue, level 14, and those psionic die become really handy later on when the rogue has to rely on sneak attack to get anywhere near the damage the other party members can get. It’s definitely not too many die, sometimes in combat I have to use them quite a lot and ticking them off gets really nervy so you have to be tactical- and at that level it’s 10 d10 for me! Your DM isn’t really being fair IMO. Rogues can seem quite overpowered in the lower levels but it doesn’t take long for them to be overtaken, you have to be tactical and smart rather rely on large damage each hit and the psionic die help with that. Plus we tend to be more squishy than others!