head to head
Marathon asks more than Call of Duty: Modern Warfare 2, and the gap is variance.

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

Execution · Competitive PvP
Aim duels against human crews layered over hidden-information loot gambles and extraction timing.
Call of Duty: Modern Warfare 2 leans Execution (Competitive PvP); Marathon leans Execution (Competitive PvP).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Call of Duty: Modern Warfare 2
Fast time-to-kill rewards raw aim and reflex
Marathon
Gunfights against other crews reward raw aim heavily
Marathon leans a little harder on reads, though the gap is small.
Call of Duty: Modern Warfare 2
Outguessing human rotations and flanks
Marathon
Predicting human crews' rotations and ambushes is constant
Marathon leans clearly harder on variance.
Call of Duty: Modern Warfare 2
Spawn flips and killstreak randomness
Marathon
Loot spawns and unseen squads create hidden information
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
Marathon
Loadout economics and extraction routing sit underneath
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.