head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; Silent Hill: Book of Memories demands more variance.

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

Optimization · Practiced Mastery
A dungeon-crawler spin-off testing build management across randomised otherworlds.
Grand Theft Auto V leans Execution (Practiced Mastery); Silent Hill: Book of Memories leans Optimization (Practiced Mastery).
Grand Theft Auto V leans a little harder on execution, though the gap is small.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Silent Hill: Book of Memories
Twin-stick melee and dodge timing matter moderately
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Silent Hill: Book of Memories
Monsters follow simple scripted aggression
Silent Hill: Book of Memories leans clearly harder on variance.
Grand Theft Auto V
Some mission and lobby randomness.
Silent Hill: Book of Memories
Procedural dungeon layouts and loot rolls vary each run
Silent Hill: Book of Memories leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
Silent Hill: Book of Memories
Karma builds, weapon upkeep and puzzle rooms reward system mastery
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.