Hi, it seems that the problem is not related to wxpython + GTK3, but just wxWidgets + GTK3. I've reported the eeschema problem some weeks ago in launchpad [1] and one of the developers wrote that.
[1] https://bugs.launchpad.net/kicad/+bug/1764646
- Bug#899215: kicad: eeschema is sluggish David Tomaschik
- Bug#899215: kicad: eeschema is sluggish Carsten Schoenert
- Bug#899215: Fabián Inostroza
