head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; The Final Station demands more variance.

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

Optimization · Practiced Mastery
Managing scarce resources between stations while clearing scripted infected with careful shots.
Grand Theft Auto V leans Execution (Practiced Mastery); The Final Station 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.
The Final Station
Headshotting infected swarms with scarce ammo demands steady aim
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
The Final Station
Infected follow simple scripted rushes, never adapt
The Final Station leans clearly harder on variance.
Grand Theft Auto V
Some mission and lobby randomness.
The Final Station
Unknown station layouts and loot until explored, then mapped
The Final Station leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
The Final Station
Rationing ammo, food and passenger care is the real game
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.