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 skill plus constant prediction of a human opponent's tendencies.

Reads · Competitive PvP
The Wii entry whose slower pace and infamous random tripping pushed Smash toward defensive mind games.
FIFA 17 leans Execution (Competitive PvP); Super Smash Bros. Brawl leans Reads (Competitive PvP).
FIFA 17 leans a little harder on execution, though the gap is small.
FIFA 17
Dribbling, shooting and defending inputs decide individual 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 17
Human opponents online keep shifting attacking and defending habits
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 17
Bounces, deflections and finishing RNG swing tight matches
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 17
Squad chemistry, formations and meta mechanics are studied layers
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.