I do no damage at all

I am currently on expert difficulty using strategic sword. I have the best inner ways, unlocked every talent and evey upgrade. The problem is tgat bosses take like a billion hits to kill. From what i have seen the problem is not the fact that i do low damage numbers, but they simply have too much health. Even normal enemies i struggle to kill. I dont know if its the difficulty because i have seen people on legend killing bosses faster and with lower damage numbers