> applications get confused

Haven't had that yet. I thought of a single application the whole time, aka. kiosk, then it shouldn't matter.

In ye olden times, when most X11 applications understood "-geometry" and didn't try to do too much in absence of WM, things worked.

Chromium and possibly others (Chromium is just what I have personally dealt with) was confused about what did it mean to be fullscreen, and various other ideas regarding placing itself on screen.

I did success in making it work for a time, but it was problematic.