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

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.

Optimization · Practiced Mastery
An off-road hauling simulator about planning routes and nursing heavy trucks through mud, ice and rivers.
Grand Theft Auto V leans Execution (Practiced Mastery); SnowRunner leans Optimization (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto V
Driving and shooting demand decent inputs.
SnowRunner
Throttle finesse and winch work prevent disasters.
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
SnowRunner
No opponents; terrain is the only adversary.
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto V
Some mission and lobby randomness.
SnowRunner
Mud and ice physics surprise until terrain is learned.
SnowRunner leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
SnowRunner
Truck loadouts, route planning and fuel logistics decide deliveries.
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.