You're correct in that regard. The string delay is used as a sort of pseudo-frame advantage by psychology. However, the frame disadvantage does not start until the string delay window has expired. So that's where the difficulty comes in is recognizing when the string delay has expired, and the delay differs by string by character. Such as Hayate has to commit to 3H+KK before the 3H+K connects to the opponent, so if you don't see the sweep it means they are in disadvantage.