head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; No More Room in Hell demands more variance.

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

Optimization · Practiced Mastery
Co-op survival testing resource discipline and routes under randomised item spawns.
Grand Theft Auto V leans Execution (Practiced Mastery); No More Room in Hell 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.
No More Room in Hell
Scarce-ammo headshots and melee spacing under pressure
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
No More Room in Hell
Zombies shamble on scripts without modelling players
No More Room in Hell leans clearly harder on variance.
Grand Theft Auto V
Some mission and lobby randomness.
No More Room in Hell
Dynamic objectives and random item spawns reshuffle each run
No More Room in Hell leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
No More Room in Hell
Route knowledge, resource discipline and teamwork are the real edge
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.