head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more variance; Sekiro: Shadows Die Twice demands more execution.

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

Execution · Practiced Mastery
A rhythm-parry action game about reading scripted tells with frame-tight timing.
Grand Theft Auto V leans Execution (Practiced Mastery); Sekiro: Shadows Die Twice leans Execution (Practiced Mastery).
Sekiro: Shadows Die Twice leans clearly harder on execution.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Sekiro: Shadows Die Twice
Frame-perfect parries are the entire combat system.
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Sekiro: Shadows Die Twice
Mikiri and perilous tells are scripted, not adaptive.
Grand Theft Auto V leans clearly harder on variance.
Grand Theft Auto V
Some mission and lobby randomness.
Sekiro: Shadows Die Twice
Almost no randomness; encounters are deterministic.
Sekiro: Shadows Die Twice leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
Sekiro: Shadows Die Twice
Boss decks and prosthetic choices are fully 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.