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

Optimization · Practiced Mastery
Horror about photographing ghosts at the last possible second inside a recurring dream manor.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.
Fatal Frame III: The Tormented leans Optimization (Practiced Mastery); Grand Theft Auto V 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.
Fatal Frame III: The Tormented
Fatal Frame shutter timing rewards held-nerve precision
Grand Theft Auto V
Driving and shooting demand decent inputs.
Grand Theft Auto V leans clearly harder on reads.
Fatal Frame III: The Tormented
Ghosts attack on scripted patterns
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Fatal Frame III: The Tormented leans clearly harder on variance.
Fatal Frame III: The Tormented
Ghost spawns and dream-house layout surprise first run
Grand Theft Auto V
Some mission and lobby randomness.
Fatal Frame III: The Tormented leans clearly harder on optimization.
Fatal Frame III: The Tormented
Camera upgrades and ghost patterns fully converge
Grand Theft Auto V
Heists, money loops, builds 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.