head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is reads, and it is a single point.

Execution · Competitive PvP
A combo-centric fighting game built around the breaker guessing game.

Reads · Competitive PvP
A platform fighter where edgeguards turn on reading the opponent.
Killer Instinct leans Execution (Competitive PvP); Super Smash Bros. Ultimate leans Reads (Competitive PvP).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Killer Instinct
Long combo execution and breaker timing
Super Smash Bros. Ultimate
Tech skill, edgeguards, and DI are mechanically heavy.
Super Smash Bros. Ultimate leans a little harder on reads, though the gap is small.
Killer Instinct
Combo-breaker guessing is a live mind game
Super Smash Bros. Ultimate
Adaptive opponents drive ledge and platform mind games.
Super Smash Bros. Ultimate leans a little harder on variance, though the gap is small.
Killer Instinct
Full information fighter
Super Smash Bros. Ultimate
Stage hazards and items if enabled.
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Killer Instinct
Frame data and matchup study
Super Smash Bros. Ultimate
Matchup knowledge and kill confirms 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.