You categorised it as an X11 issue. I showed you another desktop session ("KDE:") has a specific setting for this. Therefore, it is clearly not an unsolvable X11 problem, and likely an i3 problem.

You said "mechanism seems worth it". While there seems to be some work on extending it, this is not a new mechanism. A hypothetical i3 port to Wayland might very well have the same behaviour you dislike. (I wouldn't categorise sway as a port, rewrite seems more like it.)