Even though he threw slapping punches that appear light, he had to have mixed in some solid shots with them. That and it's possible that he had enough strength to make his opponents respect his power in spite of the bad technique.
Amir ' King ' Khan Khan controls range & distance pretty good. One of the reasons he's never been outboxed.
Oh yeah, I'm actually a big fan of his. He does have pretty bad hands, but I was always under the impression that punching like that actually increases the damages to your hands, but I'm sure he knows more than I would on that subject.
Could he truly control it that well if he held so much? Why could he not keep them at the end of his reach?
Deontay Wilder manages to keep oceans and continents between himself and any decent competition. He controls distance like no other.