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 · Pure Mechanics
Kart drift control and track knowledge with item luck shaking up placements.

Execution · Pure Mechanics
Motion-controlled tennis, bowling, golf, baseball and boxing built around simple swing gestures.
SuperTuxKart leans Execution (Pure Mechanics); Wii Sports leans Execution (Pure Mechanics).
SuperTuxKart leans a little harder on execution, though the gap is small.
SuperTuxKart
Drift control and line holding decide races
Wii Sports
Motion swing timing and accuracy decide every event
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
SuperTuxKart
Human online races reward mild item mind-games
Wii Sports
Casual local opponents add light mind games
SuperTuxKart leans a little harder on variance, though the gap is small.
SuperTuxKart
Item box rolls shake up placements
Wii Sports
Minor physics wobble and CPU behaviour randomness
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
SuperTuxKart
Track shortcuts and kart choice reward study
Wii Sports
Simple technique tricks like bowling spin 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.