head to head
Neither is simply harder - they are hard in different places. Nexus: The Jupiter Incident demands more variance; Portal demands more execution.

Optimization · Pure Optimization
Tactical space opera of capital-ship duels won through loadouts and targeting.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Nexus: The Jupiter Incident leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Nexus: The Jupiter Incident
Light real-time command input
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.
Nexus: The Jupiter Incident
Enemy fleets follow mission scripts
Portal
No adversary modeling player.
Nexus: The Jupiter Incident leans clearly harder on variance.
Nexus: The Jupiter Incident
Mission surprises on first encounter
Portal
Deterministic chambers; no randomness.
Portal leans a little harder on optimization, though the gap is small.
Nexus: The Jupiter Incident
Ship loadouts, subsystem targeting, and energy management
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.