head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Optimization · Pure Optimization
A speedy GBA metroidvania that doubles its castle into two mirrored layouts to untangle.

Optimization · Pure Optimization
Colour-painting terrain puzzles that resolve to finding the intended solution.
Castlevania: Harmony of Dissonance leans Optimization (Pure Optimization); Nihilumbra leans Optimization (Pure Optimization).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Castlevania: Harmony of Dissonance
Fast dashes make combat forgiving.
Nihilumbra
Some platforming timing, but forgiving throughout
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Castlevania: Harmony of Dissonance
Scripted enemies and bosses.
Nihilumbra
Enemies cannot be fought or read, only avoided
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Castlevania: Harmony of Dissonance
Minor relic and drop luck.
Nihilumbra
Hand-designed puzzles with nothing random
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Castlevania: Harmony of Dissonance
Twin-castle navigation and spellbook combos carry it.
Nihilumbra
Choosing which colour solves each terrain puzzle is the game
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.