head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is execution, and it is a single point.

Execution · Grand Arena
Asymmetric FPS-RTS hybrid where aliens and marines fight under live human commanders.

Execution · Competitive PvP
Weapon-based dueling testing spacing execution and mixup prediction against humans.
Natural Selection 2 leans Execution (Grand Arena); SoulCalibur III leans Execution (Competitive PvP).
Natural Selection 2 leans a little harder on execution, though the gap is small.
Natural Selection 2
Skulk movement and marine aim have steep ceilings
SoulCalibur III
Spacing, movement and just-frame timing demand real hands
SoulCalibur III leans a little harder on reads, though the gap is small.
Natural Selection 2
Human commanders mind-game tech and map control
SoulCalibur III
Versus humans, conditioning and throw-mixup guessing decides rounds
Natural Selection 2 leans a little harder on variance, though the gap is small.
Natural Selection 2
Symmetric maps, little randomness
SoulCalibur III
Deterministic combat with nothing hidden
Natural Selection 2 leans a little harder on optimization, though the gap is small.
Natural Selection 2
Tech trees, res flow, and lifeform timings
SoulCalibur III
Frame data, matchup study and stage knowledge run deep
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.