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
Cover-based shotgun duels testing movement execution and positional prediction in multiplayer.

Execution · Competitive PvP
Tests arena-shooter aim and map-control prediction against human lobbies.
Gears of War: Ultimate Edition leans Execution (Competitive PvP); Halo 2: Anniversary leans Execution (Competitive PvP).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Gears of War: Ultimate Edition
Wallbounce movement and gnasher duels demand real hands
Halo 2: Anniversary
Aim, grenades and movement decide every multiplayer duel
Halo 2: Anniversary leans a little harder on reads, though the gap is small.
Gears of War: Ultimate Edition
Multiplayer is constant positional mind-games around cover
Halo 2: Anniversary
Predicting human positioning and power-weapon pushes is constant
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Gears of War: Ultimate Edition
Weapon spawns timed and known; spread mildly random
Halo 2: Anniversary
Static spawns and timers leave little true randomness
Halo 2: Anniversary leans a little harder on optimization, though the gap is small.
Gears of War: Ultimate Edition
Map control and spawn timing knowledge structure matches
Halo 2: Anniversary
Weapon timers, map control and campaign routes are learnable systems
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.