head to head
Neither is simply harder - they are hard in different places. Super Mario Odyssey demands more execution; Wii Sports demands more reads.

Execution · Pure Mechanics
A 3D platformer whose joy lives in tight movement and capture-driven traversal.

Execution · Pure Mechanics
Motion-controlled tennis, bowling, golf, baseball and boxing built around simple swing gestures.
Super Mario Odyssey leans Execution (Pure Mechanics); Wii Sports leans Execution (Pure Mechanics).
Super Mario Odyssey leans clearly harder on execution.
Super Mario Odyssey
Precise platforming and capture-move tech ceiling.
Wii Sports
Motion swing timing and accuracy decide every event
Wii Sports leans clearly harder on reads.
Super Mario Odyssey
No adaptive opponents whatsoever.
Wii Sports
Casual local opponents add light mind games
Wii Sports leans a little harder on variance, though the gap is small.
Super Mario Odyssey
Almost no randomness in level design.
Wii Sports
Minor physics wobble and CPU behaviour randomness
Super Mario Odyssey leans clearly harder on optimization.
Super Mario Odyssey
Moon routes and movement tech learnable.
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.