A 1988 Holyfield would beat any of today's cruiserweights comfortably in my opinion. Holyfield was a truly great cruiserweight.
I agree that DH could have been competitive, but I doubt he could have won . If Holyfield had continued his career as CW, he could made 50-0-0 and be THE BEST EVER CW, and among the top ten THE BEST EVER P4P...... He was natural CW, moved up at HW because of money, earned a wealth, and wasted it. In any case, he was the best CW.
Holyfield at CW was something very special. The only person I'd give a shot at being very competitive at CW against Holy would be a fresh Cunningham. I think Haye attributes would get him blown out. Maybe O'neil Bell (another big strong bombing CW). Huck and everyone else, no chance. I can't say Usyk one way or the other yet. Not enough to go by.
I can not agree about Cunningham, never, never. Usyk has the potential to be great, but we have to wait, maybe two years...
Adamek was not mentioned, his HW career was a disaster, but in his prime he was quite decent CW champion. Although, I can not see him defeating Holyfield. No chance......