head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; Sine Mora EX demands more execution.

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

Execution · Practiced Mastery
A time-manipulation shmup where bullet-weaving and managing the countdown timer are the twin execution demands.
Grand Theft Auto V leans Execution (Practiced Mastery); Sine Mora EX leans Execution (Practiced Mastery).
Sine Mora EX leans clearly harder on execution.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Sine Mora EX
Time-dilation shooting and evading patterns demand responsive aim
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Sine Mora EX
No adaptive opponent; all patterns are scripted
Sine Mora EX leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
Sine Mora EX
Time penalties and power-up drops introduce run variability
Sine Mora EX leans a little harder on optimization, though the gap is small.
Grand Theft Auto V
Heists, money loops, builds learnable.
Sine Mora EX
Optimal weapon usage and time extension routing are learnable
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.