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 · Pure Mechanics
The hardest NES Castlevania, with branching routes and switchable partner characters.

Execution · Practiced Mastery
A precision metroidvania about learning fixed boss patterns and tight platforming.
Castlevania III: Dracula's Curse leans Execution (Pure Mechanics); Hollow Knight leans Execution (Practiced Mastery).
Castlevania III: Dracula's Curse leans a little harder on execution, though the gap is small.
Castlevania III: Dracula's Curse
Brutal platforming and tight whip timing throughout
Hollow Knight
Precise platforming and pogo timing dominate hard content.
Hollow Knight leans a little harder on reads, though the gap is small.
Castlevania III: Dracula's Curse
Scripted enemies and bosses only
Hollow Knight
Bosses run scripted attack pools; not adaptive.
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Castlevania III: Dracula's Curse
Minor enemy spawn wobble
Hollow Knight
Negligible; world layout is fixed.
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Castlevania III: Dracula's Curse
Partner choice, route branching, pattern memory
Hollow Knight
Charm builds and boss routes are fully 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.