thanks a lot for your quick reply & okay, that's what I understood.
But please imagine team sizes above 50-100 moderators because of very big forums - you'd have to add each moderator manually as a moderator. With a healthy employee turnover this would be an high administrative effort - which could be avoided by just adding the ability of handling reports to usergroups. As far as I can see this is the only feature you can't access without being added manually as a moderator (or is there more?).
Just my 2 cents: xenForo advertises a forum software which is able to handle forums upto 1 million members and more. Handling such a fictional large member group requires a lot of moderators. Adding moderators to a usergroup is one thing, adding them addionally as a moderator and adjusting rights also manually within this menu again doesn't seem to be logical or better said doesn't seem to be "manageable with a small administrative effort" anymore.
Regarding adding moderators individually, you would have to do this anyway if you were adding them to a moderator usergroup. What I do is have the the Moderator usergroup configured with all of the forum moderation permissions I want my moderators to have. Then when I make someone a moderator, I go into the ACP, add them via Users > Moderators and when I do this I simply tick the option "Add Moderator to User Groups" and select the Moderator usergroup. No other permissions are added on this screen, just this option. Then when I save them they become a moderator and are added to the Moderator usergroup. In the future if they are no longer a moderator they are just deleted from the list which will both remove them as a moderator and take them out of the Moderator usergroup.