Good workaround! Unfortunately there isn't a way to force the native Windows taskbar to stay below the full screen window when it loses focus, so your workaround is definitely the best way to do it. Alternatively, you can also just move the primary taskbar to a different monitor. To do that, right-click the taskbar and make sure "Lock the Taskbar" is unchecked, then just click and drag it to the bottom of another monitor.

It's not possible to add the Quick Launch toolbar to the DisplayFusion taskbar, as there isn't a Windows API for creating toolbar windows. If we're able to find a way around it in the future, we'll be sure to let you know

Thanks!