head to head
Neither is simply harder - they are hard in different places. Band of Bugs demands more variance; Portal 2 demands more optimization.

Optimization · Pure Optimization
A turn-based tactical strategy game with insect squads.

Optimization · Pure Optimization
A first-person puzzle game where seeing the solution is the whole skill.
Band of Bugs leans Optimization (Pure Optimization); Portal 2 leans Optimization (Pure Optimization).
Portal 2 leans a little harder on execution, though the gap is small.
Band of Bugs
minimal direct control, turn-based tactical movement
Portal 2
Portal placement requires some precision but timing is lenient.
Band of Bugs leans clearly harder on reads.
Band of Bugs
minor prediction versus AI and human opponents
Portal 2
No opponent; puzzles are static.
Band of Bugs leans clearly harder on variance.
Band of Bugs
random combat resolution elements
Portal 2
Puzzles are deterministic with no randomness.
Portal 2 leans clearly harder on optimization.
Band of Bugs
squad tactics and positioning deeply solvable
Portal 2
Solving the puzzle's logic IS the entire game.
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.