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
Sequel that adds a mother-daughter pair to its impossible-architecture puzzles.

Optimization · Pure Optimization
Open-ended puzzles testing vocabulary-driven creative problem-solving more than any reflex.
Monument Valley 2 leans Optimization (Pure Optimization); Scribblenauts Unlimited 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.
Monument Valley 2
Gentle touch controls, no reflexes
Scribblenauts Unlimited
Typing words is the only physical demand
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Monument Valley 2
Nothing opposes you
Scribblenauts Unlimited
Puzzle NPCs are static requests, not minds
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Monument Valley 2
Deterministic authored levels
Scribblenauts Unlimited
Puzzles are visible; nothing meaningful is hidden
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Monument Valley 2
Geometry manipulation puzzles with intended solutions
Scribblenauts Unlimited
Finding objects that satisfy puzzle constraints is creative problem-solving
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.