head to head
S.T.A.L.K.E.R.: Clear Sky asks more than Grand Theft Auto V, and the gap is variance.

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

Optimization · Practiced Mastery
A S.T.A.L.K.E.R. prequel adding a dynamic faction war across the Zone.
Grand Theft Auto V leans Execution (Practiced Mastery); S.T.A.L.K.E.R.: Clear Sky 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.
S.T.A.L.K.E.R.: Clear Sky
Punishing gunfights and anomaly navigation
Grand Theft Auto V leans a little harder on reads, though the gap is small.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
S.T.A.L.K.E.R.: Clear Sky
Faction-war AI is systemic, not adaptive to you
S.T.A.L.K.E.R.: Clear Sky leans clearly harder on variance.
Grand Theft Auto V
Some mission and lobby randomness.
S.T.A.L.K.E.R.: Clear Sky
Dynamic faction war and emission RNG hide outcomes
S.T.A.L.K.E.R.: Clear Sky leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
S.T.A.L.K.E.R.: Clear Sky
Upgrade economy and territory routing reward planning
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.