OP thinks Holyfield would beat Ali prime for prime

Wrong. It's not about mileage, but about him declining in terms of skill and not preparing properly due to the turmoils in his personal life.
In 1990 Tyson was in cahoots with that scum Don King.
Upon taking complete control of Tyson's career, Don King fired everyone from the original Catskill team that Tyson had essentially worked with since he was a kid.
Hired in their stead, were nobodies like Rory Holloway, Aran Snowel, and Jay Bright.
In the meantime, Mike had gone through several episodes of exercising erratic behavior:
- he had been divorced by Robin Givens, and during the whole process, had made death threats to her and her mother;
- he had been involved in a car accident where he was injured-postponing the Frank Bruno fight, which had an original date of October 10, 1988;
- he had been in a fist fight with ex-opponent Mitch Green which left Green's face a bloody mess, and Tyson's hand temporarily injured;
- he performed in subpar fashion against Frank Bruno;
- he would lose his sister Denise Tyson, who died tragically in her late 20's.

So by the time he faced Douglas, his former team was gone, his personal was going to pieces, his sister had died and he was working with incompetent trainers and cornermen for over a year. Proof of how bad his new team was the fact that he was struggling during training sessions, and at one point was dropped by Greg Page in a sparring session.
To make matters worse, Tyson spent the weeks prior to the fight with the local escort services.
During the fight with Douglas, Tyson was rarely making an effort to close the sizable gap, whereas against other tall opponents with reasonable jabs, such as Tucker, Holmes, Tubbs, and Biggs, Tyson had slipped the jab and followed up with a barrage of combinations coming in. We saw little or nothing of this against Douglas.
Following the match, Gil Clancy and Angelo Dundee were interviewed on HBO. Both agreed that the corner work in that fight was some of the most unprofessional that either man had seen in quite some time. Snowel was using a dissolved bag of water to try and reduce Tyson's swelling over his eyes, while calmly giving him ambiguous advice with no real instruction. All the while, Tyson sat with his head down during every break between rounds. There was clearly no interest here.

Actually it is. Unless the boxer is properly prepared, it doesn't matter.

They didn't, they declined much sooner. It was also obvious in the first Bruno fight.

Ruddock wouldn't even have landed hald the punches he did if he would have fought an 88 Tyson with Rooney in his corner.

WRONG.

A few punches are not proof. Tyson was getting hit 3 times as much after he fired Rooney. He became too cocky and arrogant seeing that he was still dominating despite not prepaing properly.

He was better than he was vs Douglas, more prepared. But nowhere near as good as when he was with Rooney.

Holmes went on to fight 2 more times for the world title (against Holyfield and McCall) and went the distance in both fights. In fact, he was close to winning it against McCall, even though he was 45/46 at that time. So he clearly wasn't shot when he faced Tyson.
Spinks was a Gold Medalist, Ring Champion, and was still considered the Lineal Champion by the entire world when he faced Tyson & was also Undefeated (31-0 with 21 KO's). Spinks was never even knocked down in his entire career, none the less knocked out until he faced Tyson. As for him being a LHW, that did not stop him from ending Holmes's 7 and a hald years unbeaten streak, just 1 fight short of Marciano's record.
Tucker was a very good boxer. His downfall was his cocaine addiction that he developed in the early 90s, but he was in good form vs Tyson.

 

Holyfield would be hell for 70s Ali, but he loses soundly to prime Ali, Holyfield struggling with an old Holmes doesn't induce confidence at all

 

Holyfield was slow compared to Patterson and never applied pressure like Frazier, he was good at countering and being inside with guys that stood in front of him like Bowe, 67 Ali would boast that Holyfield can't hit what his eyes can't see, too fast and slick for Holyfield to effectively counter, old Foreman was timing and landing on him imagine 67 Ali, in a brawl Holyfield doesn't have the firepower to stop or deter Ali who should easily be able to lead on points