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
One of the most mechanically demanding racers ever made, where mastering its physics tech is everything.

Execution · Pure Mechanics
A time-trial racer testing millisecond steering precision along studied ideal lines.
F-Zero GX leans Execution (Pure Mechanics); TrackMania United leans Execution (Pure Mechanics).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
F-Zero GX
Snaking and frame-tight control at absurd speeds
TrackMania United
Hundredth-second steering precision over stunts decides every leaderboard
F-Zero GX leans a little harder on reads, though the gap is small.
F-Zero GX
No adaptive opposition
TrackMania United
Ghost-style multiplayer never interacts with your car
F-Zero GX leans a little harder on variance, though the gap is small.
F-Zero GX
Fixed tracks, deterministic physics
TrackMania United
Tracks are perfectly deterministic
TrackMania United leans a little harder on optimization, though the gap is small.
F-Zero GX
Machine settings and advanced technique routes are mappable
TrackMania United
Finding the ideal line is a study discipline of its own
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.