head to head
Grand Theft Auto: San Andreas asks more than Army of Two, and the gap is optimization.

Execution · Practiced Mastery
A co-op third-person shooter built around two mercenaries juggling enemy aggro together.

Optimization · Practiced Mastery
A sprawling open-world crime epic with RPG-style character stats across a whole state.
Army of Two leans Execution (Practiced Mastery); Grand Theft Auto: San Andreas leans Optimization (Practiced Mastery).
Army of Two leans a little harder on execution, though the gap is small.
Army of Two
Cover shooting and co-op timing
Grand Theft Auto: San Andreas
Flying school and drive-bys need decent hands
Army of Two leans a little harder on reads, though the gap is small.
Army of Two
Aggro system is mappable, not adaptive
Grand Theft Auto: San Andreas
Gang AI is scripted, never adaptive
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Army of Two
Scripted setpieces
Grand Theft Auto: San Andreas
Territory wars and traffic add light randomness
Grand Theft Auto: San Andreas leans clearly harder on optimization.
Army of Two
Weapon upgrades and aggro manipulation
Grand Theft Auto: San Andreas
Stats, gym, weapon skill, and routes reward systematic play
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.