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

Execution · Pure Mechanics
Spectacle hack-and-slash where reflexes and combo flow drive every fight.

Execution · Practiced Mastery
Simon Belmont's SNES remake-quest with a multidirectional whip and a moody trek to Dracula.
God of War III leans Execution (Pure Mechanics); Super Castlevania IV leans Execution (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
God of War III
Combo execution and QTE timing carry combat.
Super Castlevania IV
Eight-way whip control and stair commitment test precision
God of War III leans a little harder on reads, though the gap is small.
God of War III
Bosses fully scripted spectacle.
Super Castlevania IV
Classic scripted monster patterns
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
God of War III
Almost no randomness.
Super Castlevania IV
Hidden wall meat, fixed locations
Super Castlevania IV leans a little harder on optimization, though the gap is small.
God of War III
Upgrade paths short and obvious.
Super Castlevania IV
Subweapon choice and boss pattern 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.