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

Optimization · Practiced Mastery
Open-world kung-fu action RPG starring a customizable mutant rodent in a toxic wasteland.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.
Biomutant 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.
Biomutant
Kung-fu combos and gunplay timing
Grand Theft Auto V
Driving and shooting demand decent inputs.
Grand Theft Auto V leans clearly harder on reads.
Biomutant
Creatures follow scripted behaviors
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Biomutant
Random loot and mutation drops
Grand Theft Auto V
Some mission and lobby randomness.
Biomutant leans clearly harder on optimization.
Biomutant
Build crafting across mutations, gear, and classes
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.