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

Optimization · Pure Optimization
An auto-battling deckbuilder about building a loop to defeat the Lich.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Loop Hero leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Loop Hero
Autobattler, almost no inputs.
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.
Loop Hero
Enemies follow scripts.
Portal
No adversary modeling player.
Loop Hero leans clearly harder on variance.
Loop Hero
Card draws and loot drops randomize.
Portal
Deterministic chambers; no randomness.
Loop Hero leans a little harder on optimization, though the gap is small.
Loop Hero
Deck and tile placement reward deep optimization.
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.