I read about the half of this, so if someone said this already I apologize. You can attack through the terrain and pretty handily win if you are willing.
I went toe to toe with him a few times but was having a little difficulty dealing with the poison because I wouldn't pay enough attention to what was going on and just die from that. I ended up using the hunter's axe in its extended mode using the pillars strategically and cheeseing the fact you can attack through objects. I would do a fully charged R2 through the pillar hitting the beast on the other side, a few of those and it was done. I felt a bit crappy for it but decided it was fair because he can attack through it as well and would hit me if I hugged too close to the pillar.
Bloodborne lets you know early on that enemies are just gonna do that shit towards you. "I learned it by watching you." "Ok, I'm being methodical, even tactical here... and these dickwads are hacking at me cheaply through a solid wall. I see how it's gonna be." Sure enough, it works, probably too well (I'd say it highlights some janky level design/AI). But the enemies keep exploiting it and so will I.
It's only leveling the field by playing by their rules.