head to head
Neither is simply harder - they are hard in different places. Eternal Darkness: Sanity's Requiem demands more optimization; Grand Theft Auto V demands more reads.

Optimization · Practiced Mastery
Psychological horror classic whose sanity effects mess with the player, not the meta.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.
Eternal Darkness: Sanity's Requiem leans Optimization (Practiced Mastery); Grand Theft Auto V leans Execution (Practiced Mastery).
Grand Theft Auto V leans a little harder on execution, though the gap is small.
Eternal Darkness: Sanity's Requiem
Targeted dismemberment combat, modest demands
Grand Theft Auto V
Driving and shooting demand decent inputs.
Grand Theft Auto V leans clearly harder on reads.
Eternal Darkness: Sanity's Requiem
Sanity tricks are scripted, not adaptive
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Eternal Darkness: Sanity's Requiem leans a little harder on variance, though the gap is small.
Eternal Darkness: Sanity's Requiem
Unknown sanity effects shock first-time players
Grand Theft Auto V
Some mission and lobby randomness.
Eternal Darkness: Sanity's Requiem leans clearly harder on optimization.
Eternal Darkness: Sanity's Requiem
Spell combinations and learned encounter layouts
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.