The monk comparison is interesting to me. It hadn't occured to me and I think that may have been what they were going for.
That having been said I think as a monk analogue I think they are a failure.
A monk does basically three things.
A) Survives
B) Mobility
C) Mage Killer
How does the Soul Knife do at these?
A) Lousy, they lack the monks saving throws, and (in the long run) AC.
B) Mobility. A Soul Knife can be a very mobile character. However this is on the strength of Psychic Feats and not on anything inherent in the class. Any other character with even a single PP from race, class, or feat can be as mobile. If this was an intended role for the Soul Knife they should have had a few bonus feats for it.
C) Fairly well. Not on the Monks strength of grappleing, but on the raw damage of the Soul Knifes alpha strike combined with their superior range. However they do need to hit the mages full AC with their medium BAB. And if they flub the alpha strike, their mage killing is over for that fight.
So if the Soul Knife doesn't really step into the monks shoes that leaves fighter and rogue. And they lack the signature strengths of both classes. I think they either need a Fighters BAB or 6 to 8 skill points a level (with a modified skill list) to step up as a full strength class.
I'm not sure why they didn't make the Soul Knife a fighter analouge as a Psy War plays much more like a combat cleric than a fighter.