Front of his card the stats seem alright but then his abilities are great. Regen+2 helps alleviate his lower wounds total, he puts out a big 5'' aura that denies enemies all of their demise triggers (which can potentially swing certain match ups). Assassin is fine, he may not have the weapon profiles you'd expect to get mileage out of it with but he doesn't need to kill good models to get the fast, he can potentially pick something weak off at range with spirit barrage and get a refund on his action. His own demise is pretty great, handing out his personal upgrade card to ANY friendly, yes OOK he can't be reanimated but if the enemy invests time into killing him you get to give another model regeneration and his Spirit Lantern gets to stick around even after his death. Extended reach is a good defensive ability, especially as it is not limited to protecting himself, if he is close enough to the enemy they don't get their charge attacks against anyone. Siphon power is also a strong ability, due to his actions.
The Yari has good range and an acceptable 6 stat, no built in triggers and a disappointing 2/3/4 track but if you add in that Siphon power means he can take a free suit of his choosing you can consider this to be a much stronger 3/4/5 damage track with the aid of Siphon Life on a Ram. Reposition allows him an escape option, Marked by Ancestors is not going to see use OOK.
Spirit Barrage is a weaker Stat5 2/3/4 with no free boost, but ignoring friendly fires and with the option to have free built in Divine Strike via Siphon Power. This makes it a very effective tool for handing out AoE Staggered and for picking up the finishing blow on low health models to get Assassin activated.
His Leap is lacking any built in suits but once again thats what Siphon Power is for. This means he has a very easy 6'' leap available to maneouver himself around (coupled with his 6'' movement he can make some distance) and a ram triggerfor sudden strike can get him a free attack action, something you can plan around if you have a 5Ram or 5 Mask in hand.