It is possible to dodge arrows; lowering the game difficulty may help with that, if you have not done so already. In any case, if you run far enough back in the tunnel you will not be followed.
Are there any protruding rocks or alcoves or anything you can take advantage of for cover? I don't recall any, but I wasn't looking since I was a high enough level to deal with him fairly easily. A couple times I have been able to shoot at opponents over a rock, part of a boat, etc, while their attacks were mostly blocked. If there is nothing along the walls, try backing up to the flat part of the tunnel, and see if you can still do damage if you are far enough back that arrows fired at you hit the stairs.
SoulSlayer; the door is locked behind you when you enter the temple, so AFAIK without a previous save you can not leave and come back later.