head to head
Neither is simply harder - they are hard in different places. PewDiePie's Tuber Simulator demands more variance; Portal demands more execution.

Optimization · Pure Optimization
An idle economy where optimal purchase order and room layout do everything.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
PewDiePie's Tuber Simulator leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
PewDiePie's Tuber Simulator
Tapping menus requires nothing
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.
PewDiePie's Tuber Simulator
No opponent exists to predict
Portal
No adversary modeling player.
PewDiePie's Tuber Simulator leans clearly harder on variance.
PewDiePie's Tuber Simulator
Minor event RNG around video topics
Portal
Deterministic chambers; no randomness.
Portal leans clearly harder on optimization.
PewDiePie's Tuber Simulator
View-per-cost room layouts and upgrade order are the entire game
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.