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

Execution · Practiced Mastery
The 3DS Mario Kart that added gliders, underwater driving, and kart customisation.

Execution · Practiced Mastery
A team arcade racer with no finish line, scoring takedowns and objectives in a rolling stampede.
Mario Kart 7 leans Execution (Practiced Mastery); Onrush leans Execution (Practiced Mastery).
Mario Kart 7 leans a little harder on execution, though the gap is small.
Mario Kart 7
Drift boosts, gliding, and underwater control
Onrush
Boost management and aerial takedowns need car control
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Mario Kart 7
Online lobbies reward anticipating rivals' items
Onrush
Team-based human opponents in stampede modes
Mario Kart 7 leans a little harder on variance, though the gap is small.
Mario Kart 7
Item luck shapes every race
Onrush
Chaotic pack collisions and fodder spawns
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Mario Kart 7
Kart customisation and track-specific routes
Onrush
Class roles and rush timing are learnable
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.