For one there is only one Group tool. No need to differentiate from other type of groups. Also the Group(s) are located in a sizable dockWidget, and can be made to hide in a tab… ‘element visibility groups’ would not make for a very descriptive Tab label or floating dockWidget Window title when sized down.
The clue to what Grouping does is the use of conventional ‘eye’ icon. Like either you see it or not. Also pay attention to the rollover tool tip(s) and the status bar.
With that said, I can see the Group(s) tool useful for other things where you want to group elements and apply same options - such as line color & style.
