Spinks was a light heavyweight boxer...not a proper heavyweight and Larry Holmes was past his prime and was already semi-retired for two years before he fought Tyson.
Honestly, a prime David Tua is no different from Dillian Whyte. And Josh beat him. You just have to look at who both Ike and Josh fought since Josh is in 20th fight and Ike got engulfed in the unfortunate incident after his 20th fight.
1). Josh has fought more fighters with better resumes than those Ike fought.
2). Josh has a better KO percentage and he won all his fights in style, save for the last one.
3). Josh already has two world titles.
Also, when you compare the amateur resumes of the both of them - it's like a comparison between night and day. You may point out the non-existent home-cooking at the 2012 Olympics in London but that doesn't negate the fact that he excelled at the 2011 World Amateur Boxing Championships in Baku and he was robbed in the finals against Cammarelle - he won that fight.
But people said Lennox Lewis wasn't good defensively and he had a suspect chin throughout his career. How times/stories have changed after the man beat the best America has to offer. And he beat the both of them in style.