What am I looking at?
This site performs statistical analyses using data acquired by scanning all Mythic Plus leaderboards rougly every 30 minutes. The little number below the spec or dungeon is the total number of runs according to the selected filter. The percent number on the right is the probability that the run is timed under the condition that it was completed and at least one player in the group played the specified spec. Or more formal:
Please note that the Blizzard API only exposes completed runs as reflected in the above expression. This might skew the statistic to one side or another. Therefore take the results with a grain of salt and not as a recommendation which class to invite or play.