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

Execution · Practiced Mastery
The Genesis Castlevania tours war-torn Europe with whip-wielding John Morris and spear-vaulting Eric Lecarde.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.
Castlevania: Bloodlines leans Execution (Practiced Mastery); Grand Theft Auto V leans Execution (Practiced Mastery).
Castlevania: Bloodlines leans clearly harder on execution.
Castlevania: Bloodlines
Stiff classic movement against demanding Genesis bosses
Grand Theft Auto V
Driving and shooting demand decent inputs.
Grand Theft Auto V leans clearly harder on reads.
Castlevania: Bloodlines
Scripted monsters throughout
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Grand Theft Auto V leans a little harder on variance, though the gap is small.
Castlevania: Bloodlines
Minor hidden items only
Grand Theft Auto V
Some mission and lobby randomness.
Castlevania: Bloodlines leans a little harder on optimization, though the gap is small.
Castlevania: Bloodlines
Character choice changes paths; patterns are learnable
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.