IMO this all stems from the token response of "O365 Groups is nothing more than a membership service". Groups is a perfectly viable collaboration platform. It is an interconnected set of services that allows people to get something done. That alone warrants its own app, nothing fancy just a launching point to the different services.
Our users approach Groups by going to a particular group, and working across the different services. Not going to a particular service and working across the different Groups. Thats why I also feel this move is pressure from the Teams team to drive users into Teams instead of Groups.
We use the calendars the exact same way mentioned above. Could be things like out of office calendars, major milestones, etc. This will get only worse when the ability to add appointments (with no actual email invites) to Group calendars fully rolls out (instead of everything is an invite).