The speedy person should understand that a quick jab won't ko a huge muscle guy. Logically it would be harder to interrupt someone the weaker you are (he might get punched in the face and stil be able to pull off his move) so they'd have to do more dodging.
Without interrupts you can have the slowest guy around doing spins for a matter of seconds and then wind up to deliver a massive blow while they just have to stand there watching the whole time.