head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; killer7 demands more optimization.

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

Optimization · Practiced Mastery
A surreal on-rails action adventure where seven assassin personas shoot invisible smiling bombs through a cryptic conspiracy.
Grand Theft Auto V leans Execution (Practiced Mastery); killer7 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.
killer7
Critical-point shots and reloads under pressure
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
killer7
No adaptive opposition; enemies fully scripted
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.
killer7
First-run Heaven Smile reveals and obtuse twists
killer7 leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
killer7
Persona puzzles and routes have fixed solutions
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.