I’m not sure why group FaceTime in every situation need to have a whiteboard or drawing. Perhaps it’s brainstorming or discussing details. Someone else above just gave the example of having 30+ employees on a conference call, clearly this would be an advantage in that area. I think you’re going to find out every company will vary differently in using Group FaceTime. It Doesn’t have to be a ‘serious tool’ to not be able to take advantage of something as an available feature if needed.
It's extremely rare to hold a group meeting without presenting anything or discussing a central idea.
Even with brainstorming, someone has to record the ideas for everyone to see and review. You can't have 32 people jotting their own notes of what they think they heard on the call.
Group FaceTime has no advantages over Skype, except that it's available on nearly every iOS device.