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

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

Optimization · Practiced Mastery
An action RPG where leveling means choosing which Londoners to drain.
Grand Theft Auto V leans Execution (Practiced Mastery); Vampyr 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.
Vampyr
Dodge-and-stamina melee combat with modest demands
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Vampyr
Enemies follow scripted patterns
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto V
Some mission and lobby randomness.
Vampyr
Citizen secrets are hidden until investigated
Vampyr leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
Vampyr
The feed-or-spare XP economy is the central solvable system
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.