PoE Pathfinder, Caustic Arrow, Spell builds

I have been playing a Pathfinder, Caustic Arrow Ballista poison build for a bit now and I am liking it a lot. It was not my league starter, but I am thinking of starting it next league as my only character. ( i normally roll a bunch and get bored of it in T16s.) All the gear is super cheap and available. My question is around elevating it more than it is. I think that it is pretty much at a plateau as the upgrades are super expensive, but I was hoping there was some weird interaction that I was missing that would up the DPS. Survivability is great, so no problems there. I imported my ch