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 · Pure Mechanics
Trilogy capstone whose equal-start arena multiplayer defined a console generation.

Execution · Competitive PvP
A car-soccer game testing aerial control and prediction of human opponents.
Halo 3 leans Execution (Pure Mechanics); Supersonic Acrobatic Rocket-Powered Battle-Cars 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.
Halo 3
Precision aim and grenade-melee timing
Supersonic Acrobatic Rocket-Powered Battle-Cars
Aerial car control and ball-striking precision is the lead
Supersonic Acrobatic Rocket-Powered Battle-Cars leans a little harder on reads, though the gap is small.
Halo 3
Equal-start fights reward predicting humans
Supersonic Acrobatic Rocket-Powered Battle-Cars
Predicting human opponents' positioning and rotations matters
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Halo 3
Equipment pickups and spawn variation
Supersonic Acrobatic Rocket-Powered Battle-Cars
Little randomness in deterministic physics
Halo 3 leans a little harder on optimization, though the gap is small.
Halo 3
Power-weapon timers and map control
Supersonic Acrobatic Rocket-Powered Battle-Cars
Boost management and rotation strategy form a real layer
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.