Mullin
Per Game: 18.2 ppg, 4.1 rpg, 3.5 apg, 50% FG, 38% 3PG
Per 36: 20.0 ppg, 4.5 rpg, 3.9 apg
Advanced: 54% eFG, 59% TS%, 18.8 PER, .139 WS/48
Carter
Per Game: 21.0 ppg, 5.0 rpg, 3.8 apg, 43% FG, 37.5% 3PG
Per 36: 21.5 ppg, 5.1 rpg, 3.9 apg
Advanced: 48% eFG, 53% TS%, 20.3 PER, .143 WS/48
No real advanced stats needed, even the basic stuff grade out Carter as a better player.
Moreover, Mullin played in a much faster paced league, especially that team in THAT time period. He was on the extreme end of point scoring and pace and yet still has smaller scoring numbers than Carter who played in one of the slowest leagues ever. Pretty much all the raw numbers show Carter as the better overall player while Mullin was a more efficient scorer.