The dashboard shows the current number of ratings and reviews for Stadia games on metacritic.com.
Data is updated regularly, so you can check the current leaderboards at any time and compare User Scores vs. Metascore completeness.
Note that the infographic also does not encourage over- or under-valuation of games, since the only relevant metrics are:
Number of Ratings and Reviews
Completeness of User Score and Metascore
➤ Link to the Stadia Metacritic Monitor
Have Fun with the Data!