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
Cover-shooter aim and QTE timing through scripted film setpieces.

Execution · Practiced Mastery
Weighty corridor shooting through scripted encounters with light loadout choice.
James Bond 007: Quantum of Solace leans Execution (Pure Mechanics); Killzone leans Execution (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
James Bond 007: Quantum of Solace
Cover shooting and quick-time events run on aim and timing
Killzone
Heavy gunplay still rewards aim and positioning
James Bond 007: Quantum of Solace leans a little harder on reads, though the gap is small.
James Bond 007: Quantum of Solace
Multiplayer adds modest human prediction; campaign is scripted
Killzone
Campaign Helghast follow scripts; servers are long dead
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
James Bond 007: Quantum of Solace
Setpiece encounters repeat identically
Killzone
Encounters are fixed and replayable
Killzone leans a little harder on optimization, though the gap is small.
James Bond 007: Quantum of Solace
Weapon choice and cover routes are shallow systems
Killzone
Character choice and route knowledge solve each level
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.