All those four men are undeniably better than Tyson. Especially Marciano, you'd have to be a fanboy to deny that.
They definitely don't have a better resume nor are they better H2H (Liston being the possible exception).
Ruddock was more left hand happy, wasn't he? Hard to make a case for Lewis being a world beater and not Tyson if you compare how they did against common opponents (Biggs, Golota, Bruno, Razor, Tucker). I think both are top fighters for what it's worth.
A SHW who can bang up close and get leverage on hooks and uppercuts inside. Take something special to beat him imo. Dempsey is 11th I think, would have to load up my spreadsheet again.
Marciano... champ for 3 years, 7 title defenses Tyson... champ for 3 years, 3 months, 9 title defenses Their championship accomplishments are pretty even. Less so, if you average the weights, ages and heights of his opponents. Marciano's greatest achievement was retiring at the correct time.
You're forgetting one thing, Tyson was battered senseless on a number of occasions and quit on others, Marciano was unbeaten.
But Marciano also had the highest ko percentage in heavyweight history. He also beat many ATGS. He accomplished much more than Tyson.
He was unbeaten, in part, because he bowed out after a 7 year career that was largely spent in the New England club circuit. He also never faced elite fighters of the size that Tyson was forced to face to get to the top. And don't bother sifting his record for some 210 pound ham and egger. Tyson had to face top ranked guys that 6-5, 220+, often times ex-chapms... night in and night out. Not exactly the same experience.
He beat two all time great light heavies. I don't consider Walcott an All Time Great heavyweight. Two of the three great names on his resume retired immediately after facing Marciano. They were at the bitter, tail end of their athletic careers. Some might say they were beyond that point. The third of these names went less than .500 for the short remainder of his career.
A very significant achievement, probably the most singular achievement in the history of the sport. And that's why you could count those who achieved it on one hand. Now, if RJJ had achieved this, his name would be mentioned in some p4p, top ten lists.