2 things:
First, he's not supposed to be a strong unit individually. He has 3 traits. He's meant to be a synergy piece. If he was a strong unit on his own he'd be overpowered. Not to mention one of those synergies is pirate, which considering how strong bonus econ is overall, needs to be kept at a slightly lower power level anyway.
Second: He actually is a solid unit. The "problem" is that you have to sink a bunch of items into him to make viable, especially a couple tears or a GA so he reliably gets his ult off. But what you might be forgetting with him is that his barrels apply on hit effects. On-hit items are already strong on most gunslingers but he gets that extra boost from them because his ult will spread those effects all over the field. Itemize him like you would a Kennan and you should be good if you're looking for him to carry in any way.