Groups/Clubs should have been added years ago (and has been suggested for years and years). But once more, XenForo missed their chance because it wasn't what they wanted in their script, never mind that their clients requested it and many that didn't would probably find a use for it. But by now... they missed the cruise liner and decided they'd rather ride the dinghy.
The attitude was "if they want it, they can pay someone else for it because we know what is good for them".
And no, they wouldn't be needed on a lot of boards... and before the XF whine & cheese brigade chimes in about bloating the script, nobody said it had to be built into the core. Just like XFMG, XFRM and XFES aren't built into the core. For those that wanted it, a first party solution would have been most welcome.
None of the current 3rd party add-ons are great. They each have their warts.
But having lived through the past history of XenForo and the way they implement things and then let it lay fallow, you would have been offered a bare-bones offering that if you wanted more, you were welcome to have 3rd party developers extend it for you.
In case you can't tell, yes, I'm still frustrated with what ultimately is the 1/2 arsed way that the XenForo developers implement features, stubbing it out and then expecting 3rd party developers to put meat on the bones of it. If they would take a little more time and effort, those features could be more useful without having to scrabble around for add-ons to get it to do what they should have done in the first place.
I could give you a lengthy list of "core functions" that are offered now that could be greatly improved if they had of given it some actual thought when implementing it, or heck even listening to their license users suggestions a little more closely. But I won't as I've done it in the past, and it tends to upset the natives and their chieftains.