Soulknife has access to psionic feats, which the samurai needs to take an extra feat to be able to do. And psionic feats can make the difference here with a good amount of extra damage potential.
With the soulknife able to imbue his weapon with decent stuff for free, it's a fair bit of equipment money he can spend on other things. The samurai has nothing to compare. Add in his psychic strike, as well as boosts from expending his focus and we're looking at some serious first strike power.
So the soulknife kinda wins equipment wise and damage wise. But the soulknife doesn't really get anything else. The Samurai has the fear effect but little else. Is the fear effect enough to counterbalance the massive gold advantage the soulknife gets due to not needing to buy a weapon? I think not. Fear immunity is relatively simple to obtain, and the soulknife, at lvl 20, is swinging around a +9 equivalent weapon.
The samurai will be hard pressed to match.