Anyone excluding Wladimir, Helenius, Joshua in their list doesn't have a clue. If we are talking about pure punching power.How to execute it in the ring effectively is different story.
Yes, who has Helenius beat by KO in the last five years? Helenius UD10 Michael Sprott Teper KO1 Michael Sprott
Helenius couldn't stun a glass jawed Michael Sprott who has been knocked out 20 times in his career. His power is clearly overrated.
Well, he KO'd a couple of decent *world championship level* chins before his shoulder injury. One of them KO'd current world champion. Sprott match was after injury. He is even stronger now. Here's a recent picture of him with his sparring partner while preparing against teper. https://instagram.com/p/9xoZrjMaBA/