Necro-posting in hopes of a possible enhancement in a future update.
Talking strictly Z-Wave here but I suppose it doesn't need to be.
I think the issue here is that folks (myself included) read the word "group" and just interpreted it as a selection of devices to be absolutely addressed. In fact however, what's being done is a SCENE is being created. A scene being a collection of devices with particular parameters/settings for each.
So it's great to have this ability to create scenes with mixed settings/parameters, but IMO, we also need the ability to address an ad-hoc group of devices the same way we do a single one. Such that ON will turn every device in the group ON and OFF will turn them all OFF and toggle with toggle them all, etc. There 's no ambiguity this way.
I'm confident this is going to continue being a point of confusion because the groups don't actually behave like devices at all. IMO, this functionality should be renamed to "SCENE" rather than device group. Keep a Virtual-Device based device group behaving like a single device with predictable ON/OFF behavior instead.
Not sure if you'd put Scenes under virtual devices at all though - that's a little jargon-like. Might be best to have an entire "Scenes" category.
Without that enhancement, what's the current preferred way to set a group of devices to ON all at once so they can all be tied to a single trigger?