Which KDE version is that?
My KDE runs perfectly well, no tearing, super fast, no issues with games, dual-monitor.
Believe me, I know what tearing is like and I wrote several comments on that topic during the last three years.
I cannot confirm the issues of the bug report on 5.15.x
On a sidenote, I do have minor tearing issues with compton on i3, but only since the last few major updates of compton (they also changed things related to glx_swap).