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
Timing-based rallies and human shot-prediction wrapped in party-court chaos.

Execution · Competitive PvP
Arena fighting built on baiting substitutions and timing punishes against humans.
Mario Power Tennis leans Execution (Competitive PvP); Naruto Shippuden: Ultimate Ninja Storm 3 leans Execution (Competitive PvP).
Mario Power Tennis leans a little harder on execution, though the gap is small.
Mario Power Tennis
Shot timing and court positioning decide rallies
Naruto Shippuden: Ultimate Ninja Storm 3
Substitution timing and combo confirms need decent hands
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Mario Power Tennis
Versus humans, baiting and outguessing shot placement matters
Naruto Shippuden: Ultimate Ninja Storm 3
PvP revolves around baiting substitutions from human opponents
Mario Power Tennis leans a little harder on variance, though the gap is small.
Mario Power Tennis
Gimmick courts and items inject chaos into points
Naruto Shippuden: Ultimate Ninja Storm 3
Support meter and item randomness barely matter
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Mario Power Tennis
Character matchups and shot selection reward modest study
Naruto Shippuden: Ultimate Ninja Storm 3
Team composition and awakening knowledge add a thin layer
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.