head to head
Neither is simply harder - they are hard in different places. Call of Duty: Modern Warfare 2 demands more variance; Tekken 6 demands more reads.

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

Execution · Competitive PvP
A combo-heavy 3D fighter where lab-trained hands meet live human prediction.
Call of Duty: Modern Warfare 2 leans Execution (Competitive PvP); Tekken 6 leans Execution (Competitive PvP).
Tekken 6 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
Tekken 6
Bound combos and movement push a high physical ceiling
Tekken 6 leans clearly harder on reads.
Call of Duty: Modern Warfare 2
Outguessing human rotations and flanks
Tekken 6
Rage comebacks amplify the human guessing game
Call of Duty: Modern Warfare 2 leans clearly harder on variance.
Call of Duty: Modern Warfare 2
Spawn flips and killstreak randomness
Tekken 6
Visible state; nothing meaningfully random
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
Tekken 6
Optimal bound routes and punishment charts are lab work
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.