Ok so i know there's a armor rating cap of 567. So if you smith something with a rating higher those extra numbers are meaningless. So i wonder if its the same thing with weapons?

I don;t think so. On a recent character I had weapon damages around 1000 (a couple mods contributed greatly to this) and could one-hit most enemies. I don't think damage has a cap, unless you get into stupidly high values, then it may glitch out.

Technically speaking, there's an upper limit of 2,147,483,647 to the damage value, as it's stored as a 32-bit signed integer. Any number higher than that will cause the damage value to overflow and become a negative value, which will cause all kinds of glitchy behavior.