head to head
Dirt 3 asks more than TrackMania 2: Stadium, and the gap is variance.

Execution · Practiced Mastery
Precise rally car control over stages that reward memorisation and tuning.

Execution · Pure Mechanics
Grinding deterministic tracks for the perfect line and the flawless run.
Dirt 3 leans Execution (Practiced Mastery); TrackMania 2: Stadium leans Execution (Pure Mechanics).
TrackMania 2: Stadium leans a little harder on execution, though the gap is small.
Dirt 3
Car control on loose surfaces is a high physical ceiling
TrackMania 2: Stadium
Perfect inputs ARE the game - hundredths decide leaderboards
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Dirt 3
Racing the clock or scripted AI, nobody adapts
TrackMania 2: Stadium
Ghost racing - opponents never interact with your run
Dirt 3 leans clearly harder on variance.
Dirt 3
Surface conditions and minor physics noise per run
TrackMania 2: Stadium
Fully deterministic physics, identical track every attempt
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Dirt 3
Stage knowledge and setup tuning reward study
TrackMania 2: Stadium
Finding the optimal racing line is half the hunt
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.