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 · Competitive PvP
An arcade soccer novelty testing timing around special-shot chaos.

Execution · Pure Mechanics
Motion-controlled tennis, bowling, golf, baseball and boxing built around simple swing gestures.
Mega Man Soccer leans Execution (Competitive PvP); Wii Sports leans Execution (Pure Mechanics).
Wii Sports leans a little harder on execution, though the gap is small.
Mega Man Soccer
Sluggish controls still reward shot timing and positioning
Wii Sports
Motion swing timing and accuracy decide every event
Mega Man Soccer leans a little harder on reads, though the gap is small.
Mega Man Soccer
Human opponents add light positional guessing
Wii Sports
Casual local opponents add light mind games
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Mega Man Soccer
Special-shot chaos adds some randomness
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.
Mega Man Soccer
Team composition and special-shot management are shallow systems
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.