I'd like to comment on your observations about Group Bulb Dimmer. As you observed, it's an amalgam of multiple possible devices used in a Group, a switch, a dimmer, and RGB bulb, an RGBW bulb, and a ColorTemperature bulb. You propose that each should have it's own dedicated driver / device type. I understand that.
However, there is a problem: Group-2.1 creates a virtual device that represents the Group. Suppose you have a Group with just dimmers and switches. There is a device that represents that Group. Now, you want to add a color bulb to the Group. How can you do that? The device that was created, were it a Group Dimmer, would not support a color bulb at all. Suppose further that you've used the Group device in several automations. We can't delete the Group dimmer device and create a new device that includes color, as that would blow up all of those automations. This is why we use the Group Bulb Dimmer for all Groups, as it can support any Group, including one that evolves from an existing Group. [Could the hub be smart enough to swap the driver on the existing device instead? Perhaps, but for now changing a driver is not something the hub supports an app to do.]
As for Dashboards and the Group device. It is not that difficult to change the template used on a tile. If all you have are dimmers, you can just select the Dimmer template, and it will display those attributes of a Group Bulb Dimmer as you want. [Could the Dashboard be smarter about how it selects the template for a Group device? Perhaps, but for now it does not.]
I do not recommend that you change the driver for the Group device in any circumstances. These are child devices that have an intimate code relationship with the app that created them, and that relationship will most likely become corrupted if you change the driver. Older versions of these drivers exist, because there are older versions of this app, and these may still be in use. We try not to just jerk things out from under people as the platform evolves. So my advice is to leave the Group device driver alone, and deal with the issues it creates in Dashboards in the Dashboard. The fact that the device page for such a device has additional commands that may not be relevant for a given group should not be a concern.
