head to head
Neither is simply harder - they are hard in different places. Portal demands more execution; Tiny Metal: Full Metal Rumble demands more reads.

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

Optimization · Pure Optimization
A turn-based tactics game about maneuvering units to outmatch the enemy.
Portal leans Optimization (Pure Optimization); Tiny Metal: Full Metal Rumble leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Portal
Portal placement timing modest.
Tiny Metal: Full Metal Rumble
Issuing unit orders has no twitch demand
Tiny Metal: Full Metal Rumble leans clearly harder on reads.
Portal
No adversary modeling player.
Tiny Metal: Full Metal Rumble
Human opponents reward predicting their advances
Tiny Metal: Full Metal Rumble leans clearly harder on variance.
Portal
Deterministic chambers; no randomness.
Tiny Metal: Full Metal Rumble
Some combat rolls and fog add uncertainty
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.
Tiny Metal: Full Metal Rumble
Unit composition, terrain and economy decide battles
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.