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

Optimization · Pure Optimization
Planning optimal squad loadouts and synchronized room entries against scripted enemies.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Breach & Clear leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Breach & Clear
Turn-based orders remove any twitch demand
Portal
Portal placement timing modest.
Breach & Clear leans a little harder on reads, though the gap is small.
Breach & Clear
Enemy AI follows scripted placements, not adaptation
Portal
No adversary modeling player.
Breach & Clear leans clearly harder on variance.
Breach & Clear
Enemy positions unknown until breached, then mappable
Portal
Deterministic chambers; no randomness.
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Breach & Clear
Squad builds and synchronized entry plans are the 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.