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 late-90s mercenary FPS infamous for its graphic locational damage system.
Call of Duty leans Execution (Practiced Mastery); Soldier of Fortune 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
Soldier of Fortune
Fast twitch aim against fragile enemies decides everything
Call of Duty leans a little harder on reads, though the gap is small.
Call of Duty
Light multiplayer prediction; campaign AI is scripted
Soldier of Fortune
Multiplayer duels add a little human prediction
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
Soldier of Fortune
Campaign layouts and spawns are fixed
Call of Duty leans a little harder on optimization, though the gap is small.
Call of Duty
Memorising set pieces and weapon positions
Soldier of Fortune
Weapon choice and level routes are quickly learned
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.