head to head
Neither is simply harder - they are hard in different places. Digimon Story: Cyber Sleuth demands more variance; Portal demands more execution.

Optimization · Pure Optimization
Solving type matchups and digivolution trees in a turn-based system with little randomness.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Digimon Story: Cyber Sleuth leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Digimon Story: Cyber Sleuth
Turn-based menus demand no dexterity
Portal
Portal placement timing modest.
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Digimon Story: Cyber Sleuth
Enemy AI follows fixed patterns, never adapts
Portal
No adversary modeling player.
Digimon Story: Cyber Sleuth leans clearly harder on variance.
Digimon Story: Cyber Sleuth
Minor drop and encounter RNG, quickly mapped
Portal
Deterministic chambers; no randomness.
Portal leans a little harder on optimization, though the gap is small.
Digimon Story: Cyber Sleuth
Digivolution trees, type matchups and team building solve fights
Portal
Pure puzzle-solving optimization.
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.