I've always considered Holyfield a hard hitter. He just didn't load up, he threw nice short punches in combinations with good technique and weight transfer. I don't remember anybody walking through his punches. Another plus for EH is that all of his punches were "good", the jab, cross, hook, uppercut. His opponent couldn't just avoid one particular punch, all of them were effective.
Aaron Pryor ? although i wouldn't say he was a light hitter, but i don't think he was a hard hitter either. Somewhere in the middle if that fits your criteria.
Sugar Ray Leonard. Not a light hitter by any means but definitely not a powerful puncher either. Once he knew he had the other guy hurt he really goes in for the kill.
One thing Ray did as well as anyone I’ve ever seen is punctuate his combinations to end with the hardest punch. Like when he got through with two he would mid-combo be loading up to finish with the right or hook. And if he got you in trouble, he definitely had killer instinct. Smiling assassin. Just look at the Dave Boy Green finish. Wow.