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
Mechanical football control plus predicting how a human opponent attacks.

Reads · Competitive PvP
The Wii entry whose slower pace and infamous random tripping pushed Smash toward defensive mind games.
FIFA 16 leans Execution (Competitive PvP); Super Smash Bros. Brawl leans Reads (Competitive PvP).
FIFA 16 leans a little harder on execution, though the gap is small.
FIFA 16
Dribbling, defending and finishing inputs decide duels
Super Smash Bros. Brawl
Slower engine lowers the ceiling but spacing still needs hands.
Super Smash Bros. Brawl leans a little harder on reads, though the gap is small.
FIFA 16
Human opponents online adapt tactics match to match
Super Smash Bros. Brawl
Defensive bait-and-punish yomi dominates its floaty neutral.
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
FIFA 16
Deflections and finishing randomness swing close games
Super Smash Bros. Brawl
Random tripping injects genuine uncontrollable RNG into movement.
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
FIFA 16
Formations and squad construction reward study
Super Smash Bros. Brawl
Matchup knowledge and ledge play reward study within a campy meta.
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.