head to head
Call of Duty: Modern Warfare 2 asks more than Deathmatch Classic, and the gap is optimization.

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

Execution · Competitive PvP
A classic multiplayer deathmatch shooter distilled to pure arena combat.
Call of Duty: Modern Warfare 2 leans Execution (Competitive PvP); Deathmatch Classic 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
Deathmatch Classic
aim and movement decide every fight
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Call of Duty: Modern Warfare 2
Outguessing human rotations and flanks
Deathmatch Classic
human opponents predict positioning and timing
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
Deathmatch Classic
weapon and spawn randomness
Call of Duty: Modern Warfare 2 leans clearly harder on optimization.
Call of Duty: Modern Warfare 2
Killstreak economy, loadout and map knowledge
Deathmatch Classic
limited map and weapon-control knowledge
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.