This is due to the delay in camera movement relative to your character's movement. When you start a movement or change direction, the camera follows it not instantly, but with a big delay.
So when you watching a stream it looks smooth, but when you play by yourself, the game feels laggy and unresponsive. Other ARPGs don't have camera delay at all, for this very reason. When I first played the game, I was frustrated because everything feels wrong. The gameplay would be so much better without that camera delay.
The obvious solution would be to add an option to disable it. Something like that:
-> Settings -> Gameplay -> Camera smoothness
- Normal
- Low
- Disabled