head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; Need for Speed: Porsche Unleashed demands more execution.

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

Execution · Practiced Mastery
A single-marque racer tracing Porsche's history with unusually demanding handling for its series.
Grand Theft Auto V leans Execution (Practiced Mastery); Need for Speed: Porsche Unleashed leans Execution (Practiced Mastery).
Need for Speed: Porsche Unleashed leans clearly harder on execution.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Need for Speed: Porsche Unleashed
Weighty handling model punishes sloppy inputs.
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Need for Speed: Porsche Unleashed
AI racers run fixed lines.
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
Need for Speed: Porsche Unleashed
Fixed point-to-point courses; little hidden.
Need for Speed: Porsche Unleashed leans a little harder on optimization, though the gap is small.
Grand Theft Auto V
Heists, money loops, builds learnable.
Need for Speed: Porsche Unleashed
Career car trading and upgrade economy reward planning.
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.