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 · Pure Mechanics
Portable FPS gunfights resting on aim with a loadout-economy wrapper.

Execution · Competitive PvP
Large-battle aim and positioning with light prediction against human players.
Killzone: Mercenary leans Execution (Pure Mechanics); Star Wars: Battlefront II leans Execution (Competitive PvP).
Killzone: Mercenary leans a little harder on execution, though the gap is small.
Killzone: Mercenary
Handheld aim and movement still decide every firefight
Star Wars: Battlefront II
Aimbot dominates infantry fights and starfighter dogfights
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Killzone: Mercenary
Multiplayer rewards reading enemy rotations and habits
Star Wars: Battlefront II
Human opponents in multiplayer create modest prediction play
Star Wars: Battlefront II leans a little harder on variance, though the gap is small.
Killzone: Mercenary
Spawns and encounters add modest unpredictability
Star Wars: Battlefront II
Spawns, vehicle availability and hero pickups add chaos
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Killzone: Mercenary
Loadout economy and contract play tune the earnings loop
Star Wars: Battlefront II
Class choice and map control reward learned plans
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.