head to head
Neither is simply harder - they are hard in different places. Championship Manager 2008 demands more variance; Portal demands more execution.

Optimization · Pure Optimization
A football management sim about building squads and optimizing tactics against variance.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Championship Manager 2008 leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Championship Manager 2008
Menu management requires no physical skill
Portal
Portal placement timing modest.
Championship Manager 2008 leans clearly harder on reads.
Championship Manager 2008
Opponent AI tactics are somewhat predictable patterns
Portal
No adversary modeling player.
Championship Manager 2008 leans clearly harder on variance.
Championship Manager 2008
Match results and injuries carry significant randomness
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.
Championship Manager 2008
Squad building, tactics and transfers are the deep 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.