head to head
Neither is simply harder - they are hard in different places. Endless Legend demands more variance; Portal demands more execution.

Optimization · Pure Optimization
Fantasy 4X with strong asymmetric factions and quest paths.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Endless Legend leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Endless Legend
turn-based
Portal
Portal placement timing modest.
Endless Legend leans clearly harder on reads.
Endless Legend
scripted AI, limited MP
Portal
No adversary modeling player.
Endless Legend leans clearly harder on variance.
Endless Legend
quest and tech rolls
Portal
Deterministic chambers; no randomness.
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Endless Legend
faction-specific yield optimization
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.