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

Optimization · Pure Optimization
A first-person puzzle game where seeing the solution is the whole skill.

Optimization · Pure Optimization
Maxis simulation where you guide a black ant colony to conquer a suburban yard.
Portal 2 leans Optimization (Pure Optimization); SimAnt leans Optimization (Pure Optimization).
Portal 2 leans a little harder on execution, though the gap is small.
Portal 2
Portal placement requires some precision but timing is lenient.
SimAnt
Light direct ant control; spider dodging is mild dexterity.
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Portal 2
No opponent; puzzles are static.
SimAnt
Red colony AI is scripted behaviour, never models you.
SimAnt leans clearly harder on variance.
Portal 2
Puzzles are deterministic with no randomness.
SimAnt
Spider, rain, lawnmower and yard events are random hazards.
Portal 2 leans clearly harder on optimization.
Portal 2
Solving the puzzle's logic IS the entire game.
SimAnt
Caste ratios, pheromone trails and expansion order are solvable.
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.