head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is execution, and it is a single point.

Execution · Practiced Mastery
Slow-motion gunfights against aggressive but ultimately mappable squad AI.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.
F.E.A.R. 3 leans Execution (Practiced Mastery); Grand Theft Auto V leans Execution (Practiced Mastery).
F.E.A.R. 3 leans a little harder on execution, though the gap is small.
F.E.A.R. 3
Slow-mo gunplay still rewards fast accurate aim
Grand Theft Auto V
Driving and shooting demand decent inputs.
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
F.E.A.R. 3
Squad AI flanks convincingly but follows mappable routines
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
F.E.A.R. 3
Encounter layouts are scripted-but-unknown first time
Grand Theft Auto V
Some mission and lobby randomness.
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
F.E.A.R. 3
Cover usage and power timing are quickly learned
Grand Theft Auto V
Heists, money loops, builds learnable.
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.