The "Reply to Sender" turns out to be valuable when someone in the group wants a response that the rest of the group might not have any interest in reading. (Granted they could Mute the reply, a terrific feature!)
One of my groups is a neighborhood list and often a member has something in the garage they want to give away. A "reply to Sender" link lets the 20 people respond privately ("I want it!!) and not to the list.
Agree about "Reply to Moderators" -- not terribly useful.
I can't imagine what earthly purpose the "Reply to Sender," or "Reply to Moderators," options at the Group Level would have if a group is to function as a group.