A barchart might be better as the comparison of instances with the most subscribed accounts doesn't mean much I feel
we have some users that register but are inactive and/or are infrequently active which could be a sign of lurkers or bots but empty accounts don't mean much when it comes to the health of an instance.
However; if we look at each community's active monthly and daily users it can tell another story and that data compared against Reddit's could be useful for anyone seeking alternatives
I'm rambling with little sleep but hopefully what I've said make a little bit of sense