head to head
Arma 2 asks more than Tom Clancy's Rainbow Six: Vegas, and the gap is variance.

Execution · Competitive PvP
A sprawling military simulator where realistic ballistics and planning beat reflexes.

Execution · Competitive PvP
Tactical gunfights testing aim, entry planning and prediction of human opponents online.
Arma 2 leans Execution (Competitive PvP); Tom Clancy's Rainbow Six: Vegas leans Execution (Competitive PvP).
Tom Clancy's Rainbow Six: Vegas leans a little harder on execution, though the gap is small.
Arma 2
Ballistics, stance, and positioning over twitch aim
Tom Clancy's Rainbow Six: Vegas
Aim and snap-to-cover gunplay punish slow hands
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Arma 2
Human squads in PvP scenarios adapt
Tom Clancy's Rainbow Six: Vegas
Multiplayer angles and pushes demand reading human opponents
Arma 2 leans clearly harder on variance.
Arma 2
Vast terrain hides enemy positions
Tom Clancy's Rainbow Six: Vegas
Terrorist hunt spawns vary modestly between runs
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Arma 2
Doctrine, loadouts, and mission planning
Tom Clancy's Rainbow Six: Vegas
Room-entry planning and map knowledge are studyable
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.