head to head
Neither is simply harder - they are hard in different places. Lost and Found Co. demands more variance; Portal demands more execution.

Optimization · Pure Optimization
A cozy hidden-object adventure testing visual search and light puzzle solving.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Lost and Found Co. leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Lost and Found Co.
Clicking objects, no twitch skill
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.
Lost and Found Co.
Solo, no adaptive opponent
Portal
No adversary modeling player.
Lost and Found Co. leans clearly harder on variance.
Lost and Found Co.
Item locations hidden until searched
Portal
Deterministic chambers; no randomness.
Portal leans clearly harder on optimization.
Lost and Found Co.
Systematic searching and puzzle-solving is the loop
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.