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

Execution · Pure Mechanics
Arcade car control across loose surfaces, weather and door-to-door packs.

Execution · Practiced Mastery
Cornering execution over memorisable circuits, with light prediction in wheel-to-wheel multiplayer.
Dirt 5 leans Execution (Pure Mechanics); Grid 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.
Dirt 5
Sliding off-road cars on mixed surfaces is the whole test
Grid 2
Car control through corners is the entire moment-to-moment test
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Dirt 5
Pack racing adds light wheel-to-wheel jockeying
Grid 2
Online wheel-to-wheel adds light positional prediction
Dirt 5 leans a little harder on variance, though the gap is small.
Dirt 5
Dynamic weather shifts grip unpredictably
Grid 2
Tracks are fixed and fully visible
Grid 2 leans a little harder on optimization, though the gap is small.
Dirt 5
Car class knowledge and line choice reward study
Grid 2
Racing lines, braking points and car selection are studyable
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.