As you can see from the graph support for measuring monthly active users was added fairly recently, so some servers might not be reporting it and in general 6m active users is a better metric, in that case that’s somewhere around 2.5 times bigger , pixelfed is around 63K 6M MAU and is also growing , two of these projects are comparable in size of use and manage to generate growth.
Sometimes it is better to look at trends and not the current market share, because that might be the result of historical circumstances that are not related to how a project or business is managed, for example writefreely already had a strong open source competitor (wordpress) and lemmy basically got a free marketing campaign due to reddit API fiasco.