head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; The Suffering demands more optimization.

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

Optimization · Practiced Mastery
An action horror game where a death-row inmate fights execution-themed monsters during a prison island breakout.
Grand Theft Auto V leans Execution (Practiced Mastery); The Suffering leans Optimization (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.
The Suffering
Fast shooting and the Insanity transformation reward sharp play
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
The Suffering
Malefactors attack on fixed archetype patterns
The Suffering leans a little harder on variance, though the gap is small.
Grand Theft Auto V
Some mission and lobby randomness.
The Suffering
Unknown spawns and morality outcomes on a blind run
The Suffering leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
The Suffering
Weapon choice, rage meter use, and routes 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.