Only Carwin compares to Ngannou in terms of lethality.
But Ngannou's power is not just one big punch. He's got massive power in both hands , devastating leg kicks, and his grappling strength is also phenomenal.
Overeem was like hugging a tree when he tries to wrestle and clinch with him, Blaydes couldn't keep him on the ground at all, and Hamilton ( massive HW, wrestler and BJJ black belt) got brute force thrown on the canvas and ended with a kimura.
His GnP is messy but is one of the most brutal I've seen (see Mihailovic, or the 2nd Blaydes fight).