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 · Practiced Mastery
A linear western shooter testing aim and learned encounter pacing through scripted set pieces.

Execution · Practiced Mastery
Weighty corridor shooting through scripted encounters with light loadout choice.
Call of Juarez: Bound In Blood leans Execution (Practiced Mastery); 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.
Call of Juarez: Bound In Blood
Aimbot would trivialise the gunfights and showdown duels
Killzone
Heavy gunplay still rewards aim and positioning
Killzone leans a little harder on reads, though the gap is small.
Call of Juarez: Bound In Blood
Scripted campaign enemies; thin multiplayer adds little prediction
Killzone
Campaign Helghast follow scripts; servers are long dead
Call of Juarez: Bound In Blood leans a little harder on variance, though the gap is small.
Call of Juarez: Bound In Blood
Encounter layouts are unknown on first run, then fixed
Killzone
Encounters are fixed and replayable
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Call of Juarez: Bound In Blood
Cover routes and concentration-mode usage are learnable patterns
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.