2K meticulously controls OVR via the Intangibles attribute, it has nothing to do with Mitchell's performance-based Attributes and Badges. He is 88 because they want him at 88.
Top 10 Shooting Guards
94 - James Harden (24.5 PER, 62 TS%, 44 AST%, 28 USG%)
90 - Devin Booker (19.2 PER, 59 TS%, 21 AST%, 33 USG%)
89 - Bradley Beal (22.7 PER, 59 TS%, 21 AST%, 34 USG%)
88 - Donovan Mitchell (21.3 PER, 57 TS%, 27 AST%, 34 USG%)
88 - Paul George (20.5 PER, 60 TS%, 25 AST%, 30 USG%)
87 - Zach LaVine (21.5 PER, 63 TS%, 23 AST%, 31 USG%)
87 - Klay Thompson (16.6 PER, 57 TS%, 11 AST%, 26 USG%)
85 - C.J. McCollum (20.8 PER, 58 TS%, 23 AST%, 27 USG%)
82 - Collin Sexton (18.0 PER, 57 TS%, 23 AST%, 30 USG%)
82 - Caris LeVert (17.8 PER, 53 TS%, 25 AST%, 29 USG%)
82 - Terry Rozier (17.1 PER, 58 TS%, 20 AST%, 24 USG%)
82 - Fred VanVleet (16.8 PER, 53 TS%, 27 AST%, 24 USG%)
They have pretty spreadsheets now but still haven't the foggiest idea on how to manage them.
Not a single member of the 2K roster team can explain the 5-point gap between Devin Booker and C.J. McCollum, much less the 3-point gap between he & Zach LaVine. They fetishize certain players.