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

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

Execution · Pure Mechanics
WWII shooter remembered for its Omaha Beach landing and tense rifle duels.
Killzone: Mercenary leans Execution (Pure Mechanics); Medal of Honor: Allied Assault leans Execution (Pure Mechanics).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Killzone: Mercenary
Handheld aim and movement still decide every firefight
Medal of Honor: Allied Assault
classic FPS aim, leaning, and sniping
Killzone: Mercenary leans a little harder on reads, though the gap is small.
Killzone: Mercenary
Multiplayer rewards reading enemy rotations and habits
Medal of Honor: Allied Assault
historic multiplayer scene rewarded outguessing humans
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Killzone: Mercenary
Spawns and encounters add modest unpredictability
Medal of Honor: Allied Assault
scripted ambushes surprise only once
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
Medal of Honor: Allied Assault
encounter memorization, especially Omaha Beach
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.