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

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

Execution · Practiced Mastery
An open-world romp where the President of the United States gets superpowers inside an alien simulation.
Grand Theft Auto V leans Execution (Practiced Mastery); Saints Row IV leans Execution (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Saints Row IV
Superpowered movement and shooting are fast but forgiving
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.
Saints Row IV
Simulation enemies run fixed scripts
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto V
Some mission and lobby randomness.
Saints Row IV
Mild spawn and sandbox randomness
Saints Row IV leans a little harder on optimization, though the gap is small.
Grand Theft Auto V
Heists, money loops, builds learnable.
Saints Row IV
Power upgrade paths trivialise the simulation once optimised
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.