head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Execution · Pure Mechanics
WWII gunfight execution with light multiplayer prediction.

Execution · Pure Mechanics
Arcade soccer brawling where quick inputs and special-shot setups beat tactics.
Call of Duty 3 leans Execution (Pure Mechanics); Kunio-kun's Nekketsu Soccer League 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 3
Aimbot trivialises both campaign and multiplayer gunfights
Kunio-kun's Nekketsu Soccer League
Special shots, tackles and positioning need quick hands
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Call of Duty 3
Multiplayer adds modest human positional prediction
Kunio-kun's Nekketsu Soccer League
Versus a friend, faking shots and tackles adds 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 3
Scripted setpieces and spawn flow add minor unknowns
Kunio-kun's Nekketsu Soccer League
Weather and wacky physics add mild chaos
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Call of Duty 3
Map knowledge and weapon choice reward light study
Kunio-kun's Nekketsu Soccer League
Team picks and shot setups have learnable best answers
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.