head to head
Neither is simply harder - they are hard in different places. Imperial Glory demands more reads; Portal demands more execution.

Optimization · Pure Optimization
A Napoleonic strategy game testing empire economy and battlefield formation play.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Imperial Glory leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Imperial Glory
Pausable battles and turn-based empire management, minimal dexterity
Portal
Portal placement timing modest.
Imperial Glory leans clearly harder on reads.
Imperial Glory
Human multiplayer battles allow some feinting, AI doesn't adapt
Portal
No adversary modeling player.
Imperial Glory leans clearly harder on variance.
Imperial Glory
Diplomacy outcomes add modest uncertainty
Portal
Deterministic chambers; no randomness.
Portal leans a little harder on optimization, though the gap is small.
Imperial Glory
Economy, research and Napoleonic battle formations are the solvable core
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.