I found that an unhoned blade after sanding cuts just as good as a properly honed blade when slicing movement is involved.
This looks nasty indeed. CA would probably have kept it shut until it had healed over properly, and you wouldn't have had such a big scar. I think.

Out of curiosity (I really have no clue), what would it have costed? I can't imagine NOT going to the ER with a cut like that.

If it had been infected (althoug the blade was probably very clean) or a sinew, nerve or tendon had been partially hit, it could have had nasty consequences if left untended.