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
Open-zone gunfights where aim, ambush prediction and gear economy all matter.
Call of Duty: Modern Warfare 2 leans Execution (Competitive PvP); Stalcraft: X 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
Stalcraft: X
Gunfights against other stalkers reward raw aim and movement
Call of Duty: Modern Warfare 2 leans a little harder on reads, though the gap is small.
Call of Duty: Modern Warfare 2
Outguessing human rotations and flanks
Stalcraft: X
Open-zone PvP means predicting ambushes from adapting humans
Stalcraft: X leans a little harder on variance, though the gap is small.
Call of Duty: Modern Warfare 2
Spawn flips and killstreak randomness
Stalcraft: X
Anomalies, artifact spawns and who you meet inject randomness
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
Stalcraft: X
Gear economy, artifact builds and route knowledge compound
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.