Pound for pound not a top 5 heavy, but he is larger than the previous heavies of the seventies etc so kinda hard to say. Potentially he could he could beat most heavies who ever lived cause of his sheer size plus ring skills.
Top 5. Fought in the deepest era of powerpunchers and beat every man he faced. Mason, Ruddock, McCall, Butler, Morrison, Grant, Bruno, Tua, Briggs, Golota, Tyson (even an older one) all punched extremely hard. Guys like Holyfield, Mercer and Tucker weren't far behind. Remained at the top level of the game for a decade or more. Loss of focus was his only shortcoming but everything else complimented his physical attributes immensely. I can not think of 5 Heavies I would rank above him. Louis, Ali, maybe Holmes, but that's about it.
Never got off the floor to win a fight. Once Lewis was down...that was it. He was not great much less top 5.
I don't understand why people focus on him not getting off the canvas, rather than the small number of times he actually was on the canvas. Twice in a career is less than Foreman and Frazier had in one fight. Tyson was also down more, as was Liston and many others.
You seem to overlook Tyson's emphatic rise to the top, the aura of invincibility and his record (still intact) of becoming youngest HW champion. He beat Trevor Berbick to win the title who was one of the top HWs at the time. Tyson never reached his potential as a fighter but history will remember him well.