That's fine for the majority of Linux apps, but being so strict could impact cross-platform apps that don't understand those assumptions, and then they don't work well at all. For example, the interactive brokers Java application is written in a cross-platform way that makes use of many popup menus. I would hate my choice of wm saying, no, you cannot effectively use this software because it doesn't conform to our windowing constraints.

And yes, I use i3, so I am a fan of tiling windomanagers too. Not everything nicely fits into such a box though, and it's better err on the side of compatibility here, than say, can't use that app, sorry