head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; OutRun 2006: Coast 2 Coast demands more execution.

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

Execution · Practiced Mastery
Arcade drift racing testing flowing car control and memorised optimal lines.
Grand Theft Auto V leans Execution (Practiced Mastery); OutRun 2006: Coast 2 Coast leans Execution (Practiced Mastery).
OutRun 2006: Coast 2 Coast leans clearly harder on execution.
Grand Theft Auto V
Driving and shooting demand decent inputs.
OutRun 2006: Coast 2 Coast
Sustained drift control at speed is the heart of it
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
OutRun 2006: Coast 2 Coast
Traffic is patterned, not predictive
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
OutRun 2006: Coast 2 Coast
Route branches you choose yourself - nothing hidden
OutRun 2006: Coast 2 Coast leans a little harder on optimization, though the gap is small.
Grand Theft Auto V
Heists, money loops, builds learnable.
OutRun 2006: Coast 2 Coast
Perfect drift lines and route choice are learnable theory
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.