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

Optimization · Pure Optimization
Colour-painting terrain puzzles that resolve to finding the intended solution.

Optimization · Practiced Mastery
A co-op yarn puzzle-platformer where two tethered characters solve levels together.
Nihilumbra leans Optimization (Pure Optimization); Unravel Two 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.
Nihilumbra
Some platforming timing, but forgiving throughout
Unravel Two
Light platforming plus two-character swing coordination
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Nihilumbra
Enemies cannot be fought or read, only avoided
Unravel Two
No adaptive opposition, co-op only
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Nihilumbra
Hand-designed puzzles with nothing random
Unravel Two
Fixed levels, fully visible
Nihilumbra leans a little harder on optimization, though the gap is small.
Nihilumbra
Choosing which colour solves each terrain puzzle is the game
Unravel Two
Puzzles solved by routing two yarn characters together
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.