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

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.

Optimization · Pure Optimization
Lineup optimisation and deploy timing against fixed stages, gated by gacha luck.
Portal leans Optimization (Pure Optimization); The Battle Cats leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Portal
Portal placement timing modest.
The Battle Cats
Tapping deploy buttons with timing, minimal dexterity
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Portal
No adversary modeling player.
The Battle Cats
Enemy waves are fixed per stage
The Battle Cats leans clearly harder on variance.
Portal
Deterministic chambers; no randomness.
The Battle Cats
Gacha rolls gate which cats you even own
Portal leans a little harder on optimization, though the gap is small.
Portal
Pure puzzle-solving optimization.
The Battle Cats
Lineup building and deploy timing solve each stage
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.