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

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

Execution · Practiced Mastery
A twin-stick arcade shooter where flawless movement through layered projectile patterns and human-rescue routing is the skill ceiling.
Grand Theft Auto V leans Execution (Practiced Mastery); Nex Machina leans Execution (Practiced Mastery).
Nex Machina leans clearly harder on execution.
Grand Theft Auto V
Driving and shooting demand decent inputs.
Nex Machina
Rapid dodging through layered lasers and bullets is the entire test
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Nex Machina
All enemy behaviour is scripted arcade-style
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.
Nex Machina
Enemy arrangement has minor randomisation between waves
Nex Machina leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
Nex Machina
Human rescue routing and weapon pick sequencing reward study
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.