head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; Pac-Man Championship Edition DX demands more execution.

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

Execution · Practiced Mastery
Score-attack remix of Pac-Man built around herding huge ghost trains at high speed.
Grand Theft Auto V leans Execution (Practiced Mastery); Pac-Man Championship Edition DX leans Execution (Practiced Mastery).
Pac-Man Championship Edition DX leans clearly harder on execution.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Pac-Man Championship Edition DX
Blistering speed demands frame-tight cornering
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Pac-Man Championship Edition DX
Sleeping ghosts follow deterministic trains
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
Pac-Man Championship Edition DX
Board layouts are fixed and learnable
Pac-Man Championship Edition DX leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
Pac-Man Championship Edition DX
Routing ghost trains for maximum score chains
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.