You could actually make a case based on stats that Mason is the best rookie in the league this year. He has by far the leading
PER among rookies with at least 500 minutes, and actually leads Basketball Reference's
Win Shares (which is not a rate stat, i.e., it's more like 'total points' than 'points per minute'). He's also has an adjusted +/- of -0.5, vs. -2.6 for Carter-Williams, -1.1 for Burke, and -2.2 for Oladipo, who I gather are the leaders for rookie of the year. Very impressive what he's doing this year.