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
Destructible-environment shooter with tight gunplay.

Execution · Competitive PvP
Definitive competitive tactical FPS balancing aim mastery with team strategy.
Battlefield: Bad Company 2 leans Execution (Competitive PvP); Counter-Strike: Global Offensive leans Execution (Competitive PvP).
Counter-Strike: Global Offensive leans a little harder on execution, though the gap is small.
Battlefield: Bad Company 2
Bullet drop and recoil demand real aim
Counter-Strike: Global Offensive
Spray control and flick precision at the top
Counter-Strike: Global Offensive leans a little harder on reads, though the gap is small.
Battlefield: Bad Company 2
Destruction and flanks punish positional reads
Counter-Strike: Global Offensive
Anti-stratting and mid-round adaptation
Counter-Strike: Global Offensive leans a little harder on variance, though the gap is small.
Battlefield: Bad Company 2
Some vehicle/spawn randomness, mostly skill
Counter-Strike: Global Offensive
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Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Battlefield: Bad Company 2
Class kits and gadgets optimize objectives
Counter-Strike: Global Offensive
Utility lineups, economy, and default strats
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.