This list is sorted, you don't have to click through all pages, just jump to
page 24800 or whatever.
More than 3 million different characters with at least one completed mythic+
A score of 800 is achieved by timing all +10s, about 0.5 million characters have this score. A score of 1280 means timing all +15s, about 0.09 million chars. If you timed all +10s your char is in the top 17% of all, if you timed all +15s in the top 2.7% (and so are you as a player assuming all players have a similar amount of Alts).
So yeah, 83% aren't even doing +10 and I think no matter how you look at it that's "most players".