Before making so many calculations, why don’t you try out some PvP? If you calculate the stats for all sets, mages always get more because they are more squishy. It doesn’t mean they are more overpowered 🙂 Tattoo of Soul is being carefully measured, so don’t worry about this. I am actually considering a way of increasing archer’s atk speed a bit more when using this tattoo.
The nerf came because daggers were getting crazy attack speeds. As I said, this is not a final change, so don’t worry about it so much.
But as I said, don’t focus so much on the maths. Play the game, if you see anything wrong with it while playing then report it. 4% and 20% and 50% don’t mean anything on their own.