In 10.1 that default Group Home page just consists of the Set Up Your Community/Group widget. Once that is run the Home page for the group is set to a real group page layout. Where is that real group home page layout defined?
But after you run the setup the home page for that group becomes a customized home page for that group. And that home page has a layout and widgets in it. The layout and widgets for that custom home page came from some configuration somewhere. I was thinking that maybe it was defined in the template-group-home-groups.xml file that is in the Setup your community/group widget. But that doesn't seem to be it.
I have discussed changing the Group Theme default page to be the page layout we want, but my business owner likes the group creation automation of the Setup widget. But it leaves him having to change the home page settings for every site after the setup is complete. The other page templates are fine because those we can set in the default group theme.
Actually I don't think so. I had been looking at the wrong XML file in the Setup your community/group widget. I should have looked at template-group-home-default.xml rather that template-group-home-groups.xml. I updated that file with the widgets I wanted and saved the Setup your community/group widget. Then created a new group using the setup widget. The resulting home page had the new widgets I added in the template-group-home-default.xml file of the setup widget.