head to head
Neither is simply harder - they are hard in different places. Portal demands more execution; Tastee: Lethal Tactics demands more reads.

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

Optimization · Pure Optimization
A simultaneous-turn tactics game testing positioning and predicting opponent commitments.
Portal leans Optimization (Pure Optimization); Tastee: Lethal Tactics leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Portal
Portal placement timing modest.
Tastee: Lethal Tactics
Planning phase, no twitch aiming required
Tastee: Lethal Tactics leans clearly harder on reads.
Portal
No adversary modeling player.
Tastee: Lethal Tactics
Simultaneous turns reward predicting human opponent moves
Tastee: Lethal Tactics leans clearly harder on variance.
Portal
Deterministic chambers; no randomness.
Tastee: Lethal Tactics
Low randomness, mostly deterministic resolution
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Portal
Pure puzzle-solving optimization.
Tastee: Lethal Tactics
Precise positioning and timing of merc actions
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.