Flatpak is optional, it's just setup out of the box so if you want to flatpak install stuff it just works. Their app center also shows flatpaks but has a drop down where you can pick either the deb or flatpak version if both are available.

And the tiling extension is off by default. It's just a little toggle in the (very nice) settings dialog to turn it on or off. You can totally uninstall it too as it's just a regular gnome extension (and you can even install it right now on non-pop gnome 3 systems).