On the MMR page of the site, the author has collected information from the roughly 4.5 million accounts that have their accounts set to publically share information about rank and games. According to this data, the median — a form of average derived from the middle value — of all Dota 2 ranks is currently Crusader 5.
According to the Dota 2 Wiki, a rank of Crusader 5 equates to about 2400 MMR using the old, number-based system. This number has not shifted dramatically over the years, as a blog post from Valve back in 2013 reported roughly the same information.
If you’re wondering how you measure up against other players, here are some stats:
— Crusader 2: 30th percentile
— Crusader 4: 40th percentile
— Archon 1: 50th percentile
— Archon 3: 60th percentile
— Archon 5: 70th percentile
— Legend 2: 80th percentile
— Legend 5: 90th percentile
While the creator of the site himself admits that the dataset isn’t conclusive, this likely is as complete of a picture as we’ll ever get without Valve giving us the information. MMR has always been a highly debated subject but it seems like the distribution throughout ranks does not really shift, and if it does, it does so very slightly.