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

Execution · Pure Mechanics
Party racing and arena shootouts decided mostly by platforming speed.

Execution · Pure Mechanics
A 3D platformer whose joy lives in tight movement and capture-driven traversal.
Rayman Arena leans Execution (Pure Mechanics); Super Mario Odyssey leans Execution (Pure Mechanics).
Super Mario Odyssey leans clearly harder on execution.
Rayman Arena
Footrace platforming speed and arena aim decide matches
Super Mario Odyssey
Precise platforming and capture-move tech ceiling.
Rayman Arena leans clearly harder on reads.
Rayman Arena
Human rivals add light jockeying, little depth
Super Mario Odyssey
No adaptive opponents whatsoever.
Rayman Arena leans a little harder on variance, though the gap is small.
Rayman Arena
Minor pickup randomness in arenas
Super Mario Odyssey
Almost no randomness in level design.
Super Mario Odyssey leans clearly harder on optimization.
Rayman Arena
Track knowledge gives a modest edge
Super Mario Odyssey
Moon routes and movement tech 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.