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

Optimization · Pure Optimization
A tactical RPG where careful positioning and managing randomized combat odds decides survival.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Fire Emblem leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Fire Emblem
no real-time physical skill, turn-based
Portal
Portal placement timing modest.
Fire Emblem leans a little harder on reads, though the gap is small.
Fire Emblem
AI is scripted, no true adaptation
Portal
No adversary modeling player.
Fire Emblem leans clearly harder on variance.
Fire Emblem
hit chance rolls are heavily randomized
Portal
Deterministic chambers; no randomness.
Fire Emblem leans a little harder on optimization, though the gap is small.
Fire Emblem
permadeath tactics and builds near-solvable
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.