While i tried so hard to beat Krauser in Professional mode with 100+ attempts, i figured out an very easy way to adjust the difficulty:

- In video options, choose 60 FPS
- Use another tool to limit the FPS of your GPU to 30, eg. with RTSS for nvidia's (think AMD has something similar built-in)

With these settings, the game is running in Slo-Mo which gives you much more time to precisely aim and evade attacks by pressing combo keys or buttons in time. Of course this consumes much more real time so it is not suitable for regular gameplay, but a good plan B for bosses if you got stuck.

Have Fun.