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
A musical adventure where learning and reversing melodic spells forms a closed combinatorial puzzle system.

Optimization · Pure Optimization
A knowledge-based mystery solved by mapping a deterministic solar system.
Loom leans Optimization (Pure Optimization); Outer Wilds 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.
Loom
Musical spell sequences require accurate note input under light pressure
Outer Wilds
Light piloting, mostly forgiving
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Loom
Fantasy narrative with scripted antagonists
Outer Wilds
World is fixed; nothing adapts to you
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Loom
Deterministic world with no randomised elements
Outer Wilds
Loop is deterministic once understood
Outer Wilds leans a little harder on optimization, though the gap is small.
Loom
Learning and combining distaff spells in the correct order is a fully solvable logic system
Outer Wilds
Pure knowledge puzzle - solve the system
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.