I agree with Holmes but Douglas had fights in which he looked very good as a boxer-puncher. Tyson bout is obvious example but against Tony Tucker Buster looked also great untill he was stopped. Some hard bombs thrown there, Douglas was winning rather clearly until he was stoped by iron chined TNT. Personally I would allow Buster to continue in that one, he was dazed but it was thle last round...
Douglas never scored a KO against a ranked fighter other than Tyson. The best fighter he stopped was Mike Williams, who was a fringe contender at best. I mean, who else did he even knock down ? He wasn't a seriously hard puncher, he was average for a world-class heavyweight.
From what I saw he had serious pop in his punches and his underrated skills make me feel that he could be mentioned as a good boxer-puncher. He faced many good chinned fighters that he couldn't KO: Cobb, Berbick, Tucker, McCall. But I see your point, he doesn't belong to the greatest group representing boxer-puncher style at hw and overall it's hard to find a good heavy with this style.
Louis, Walcott, Liston, Lewis, Tyson (early version). All had good boxing skills and genuine KO power. Maybe throw Wlad and Patterson in there too.
...I...don't think Oscar ever got up as high as heavyweight, mug... Exactly. Let's do that. Just list everyone who isn't a bad boxer or puncher.