I think another way to look at it is that accounts are tightly coupled to instances, to the point of being a detriment. I've personally lost all of my data and had to start over from scratch 5 or 6 times due to servers suddenly going down over the years.
Groups are one way to abstract community functions up a level, and what's crazy is that Group Actors themselves could also have a similar thing. People have talked about merged cross-instance communities on Lemmy; this would be one way of enabling that.