head to head
Neither is simply harder - they are hard in different places. Carrion demands more optimization; Grand Theft Auto V demands more reads.

Optimization · Practiced Mastery
Reverse-horror metroidvania where you play the escaped flesh monster.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.
Carrion leans Optimization (Practiced Mastery); Grand Theft Auto V leans Execution (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Carrion
Fluid tentacle movement and snatch timing
Grand Theft Auto V
Driving and shooting demand decent inputs.
Grand Theft Auto V leans clearly harder on reads.
Carrion
Guards follow simple fixed behaviours
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Carrion
Layouts and encounters are fixed
Grand Theft Auto V
Some mission and lobby randomness.
Carrion leans clearly harder on optimization.
Carrion
Route memory and biomass upgrade puzzles
Grand Theft Auto V
Heists, money loops, builds learnable.
A matching score does not mean a matching test. Two games can both sit at 10 on execution and demand completely different things of you - which is why the reasoning above matters more than the number beside it.