When Wu Kong delivers, he delivers more than Tarlak. It’s the miss rate that hurts – particularly on big titans, where a missed stun can easily result in a dead hero (usually Wu Kong).
Wu Kong also affects special skills; Tarlak only boosts normal damage. This is good and bad. I have won some apparently hopeless war battles when a special, boosted by Wu, kills a target – without the buff, the foe would have lived. Of course, I’ve also lost “sure wins” because several specials in a row failed under Wu’s influence.
Wu may also still have a role on teams facing purple heroes, just to stack another yellow in the mix.