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 fast arcade FPS whose skill test is twitch aim plus couch-rival prediction.
Call of Duty leans Execution (Practiced Mastery); TimeSplitters 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
TimeSplitters
Fast arcade gunplay rewards twitch aim
TimeSplitters leans a little harder on reads, though the gap is small.
Call of Duty
Light multiplayer prediction; campaign AI is scripted
TimeSplitters
Local multiplayer adds human guessing; bots do not adapt
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
TimeSplitters
Spawn and pickup timing add mild uncertainty
Call of Duty leans a little harder on optimization, though the gap is small.
Call of Duty
Memorising set pieces and weapon positions
TimeSplitters
Challenge times and map control are learnable
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.