head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is execution, and it is a single point.

Execution · Competitive PvP
Blockbuster 2009 sequel famous for killstreak chains and frantic multiplayer.

Execution · Competitive PvP
Striking execution and constant human mix-up prediction across MMA phases.
Call of Duty: Modern Warfare 2 leans Execution (Competitive PvP); EA Sports UFC 5 leans Execution (Competitive PvP).
Call of Duty: Modern Warfare 2 leans a little harder on execution, though the gap is small.
Call of Duty: Modern Warfare 2
Fast time-to-kill rewards raw aim and reflex
EA Sports UFC 5
Strike timing, head movement and transition denial demand hands
EA Sports UFC 5 leans a little harder on reads, though the gap is small.
Call of Duty: Modern Warfare 2
Outguessing human rotations and flanks
EA Sports UFC 5
Out-guessing a human's strike-grapple mix is the core duel
Call of Duty: Modern Warfare 2 leans a little harder on variance, though the gap is small.
Call of Duty: Modern Warfare 2
Spawn flips and killstreak randomness
EA Sports UFC 5
Damage events and doctor stoppages add 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: Modern Warfare 2
Killstreak economy, loadout and map knowledge
EA Sports UFC 5
Stamina math and matchup study underpin the meta
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.