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 · Pure Mechanics
A two-minute test of joystick reflexes and simple punch-trading rhythm.

Execution · Competitive PvP
Wrestling crude controls to land specials while outguessing a human opponent.
Boxing leans Execution (Pure Mechanics); Street Fighter leans Execution (Competitive PvP).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Boxing
Joystick speed and punch timing decide the two-minute bout
Street Fighter
Notoriously stiff inputs make landing specials the real fight
Street Fighter leans a little harder on reads, though the gap is small.
Boxing
A human second player can be baited and predicted
Street Fighter
Human versus rounds still reward bait and punish
Street Fighter leans a little harder on variance, though the gap is small.
Boxing
Nothing hidden or random in the ring
Street Fighter
Nothing hidden between two visible fighters
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Boxing
Scoring rules are shallow; positioning tricks are quickly learned
Street Fighter
Tiny moveset leaves little system to solve
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.