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
The original 2003 WWII shooter built around cinematic squad set pieces.

Execution · Pure Mechanics
A PS4-era Killzone where a Shadow Marshal and his OWL drone fight through a divided Helghast city.
Call of Duty leans Execution (Practiced Mastery); Killzone Shadow Fall 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.
Call of Duty
Aim and reaction carry the scripted firefights
Killzone Shadow Fall
Standard FPS aim and movement ceiling
Killzone Shadow Fall leans a little harder on reads, though the gap is small.
Call of Duty
Light multiplayer prediction; campaign AI is scripted
Killzone Shadow Fall
PvP modes reward predicting human players
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Call of Duty
Some spawn and hit unpredictability
Killzone Shadow Fall
Some open level routes and spawn noise
Call of Duty leans a little harder on optimization, though the gap is small.
Call of Duty
Memorising set pieces and weapon positions
Killzone Shadow Fall
OWL drone usage and loadouts optimize cleanly
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.