head to head
Portal 2 asks more than Monument Valley 2, and the gap is optimization.

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

Optimization · Pure Optimization
A first-person puzzle game where seeing the solution is the whole skill.
Monument Valley 2 leans Optimization (Pure Optimization); Portal 2 leans Optimization (Pure Optimization).
Portal 2 leans clearly harder on execution.
Monument Valley 2
Gentle touch controls, no reflexes
Portal 2
Portal placement requires some precision but timing is lenient.
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
Portal 2
No opponent; puzzles are static.
Monument Valley 2 leans a little harder on variance, though the gap is small.
Monument Valley 2
Deterministic authored levels
Portal 2
Puzzles are deterministic with no randomness.
Portal 2 leans clearly harder on optimization.
Monument Valley 2
Geometry manipulation puzzles with intended solutions
Portal 2
Solving the puzzle's logic IS the entire 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.