head to head
Neither is simply harder - they are hard in different places. Digimon World: Next Order demands more variance; Portal 2 demands more execution.

Optimization · Pure Optimization
Modern revival of the Digimon World raising formula with two partners and mapped-but-hidden evolution rules.

Optimization · Pure Optimization
A first-person puzzle game where seeing the solution is the whole skill.
Digimon World: Next Order leans Optimization (Pure Optimization); Portal 2 leans Optimization (Pure Optimization).
Portal 2 leans clearly harder on execution.
Digimon World: Next Order
Battles are mostly automated with order timing
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.
Digimon World: Next Order
No adaptive opposition
Portal 2
No opponent; puzzles are static.
Digimon World: Next Order leans clearly harder on variance.
Digimon World: Next Order
Hidden evolution conditions and lifespan rolls
Portal 2
Puzzles are deterministic with no randomness.
Portal 2 leans a little harder on optimization, though the gap is small.
Digimon World: Next Order
Training schedules and care routines are fully solvable
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.