head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is execution, and it is a single point.

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

Execution · Practiced Mastery
Tests racing-line discipline and upgrade economy management on fixed real-world circuits.
Grand Theft Auto V leans Execution (Practiced Mastery); Real Racing 3 leans Execution (Practiced Mastery).
Real Racing 3 leans a little harder on execution, though the gap is small.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Real Racing 3
Braking points and racing lines are pure motor skill
Grand Theft Auto V leans a little harder on reads, though the gap is small.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Real Racing 3
Time-shifted opponents are recordings, not adapting minds
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
Real Racing 3
Tracks are licensed and fully fixed
Real Racing 3 leans a little harder on optimization, though the gap is small.
Grand Theft Auto V
Heists, money loops, builds learnable.
Real Racing 3
Car upgrades and the monetised economy demand managing
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.