head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is reads, and it is a single point.

Execution · Competitive PvP
Futuristic large-scale Battlefield where teams besiege flying Titan carriers.

Execution · Practiced Mastery
The sequel adding Horde mode to the campaign-plus-versus cover shooter formula.
Battlefield 2142 leans Execution (Competitive PvP); Gears of War 2 leans Execution (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Battlefield 2142
Gunplay, piloting, and Titan boarding need solid mechanics
Gears of War 2
Gnasher battles and movement tech set the ceiling
Battlefield 2142 leans a little harder on reads, though the gap is small.
Battlefield 2142
64-player human teams shift fronts and Titan assaults
Gears of War 2
Human opponents in versus drive prediction play
Battlefield 2142 leans a little harder on variance, though the gap is small.
Battlefield 2142
Large maps hide flanks; battle chaos obscures information
Gears of War 2
Horde spawns add mild randomness
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Battlefield 2142
Unlock paths, squad roles, and Titan strategy reward planning
Gears of War 2
Power-weapon timing and positioning are solvable
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.