Fishing polls do no damage. The only thing about them that is useful is the knockback... Which can actually be a life saver.
I one time got myself trapped in a corner in the water, the guy was going to block my way to the land and keep me in that corner at the same time. The only thing I had to stop him, a fishing rod... I repeatedly hit him with it, only just got to land and avoided a hit, and I managed to get away to safety. About a few minutes later, not long after my health regenerated fully, he came back and I killed him. Fishing rods are better than people make them out to be...
I always have one in my hotbar just in case, you never know when you'll need one. That tiny bit of knockback in the water makes a huge difference distance wise when you get to land. I even once broke someones boat with one.