I think that Frank Bruno in 1987 was a far more formidable opponent than THAT version of Cooney, to be honest. As for the Holmes fight, I think that we can both agree that Spinks was a different fighter in 1985 than he was in 1988.
Bruno takes out the '88 version who was annihilated by Tyson. I'd give the mid-80's Spinks a very good shout of winning. Bruno mid-round TKO.
There seem to be a general assumption here that Spinks had declined dramaticaly by the time he fought Tyson. I don't see any evidence to suport this other than his performance against Tyson.
Do I have SOLID eveidence that he was totally diminished? No. But if we look at the trends and the direction that his career was going in, then I think a reasonable assumption can be made. He clearly was beaten in his rematch against Holmes who by this point was 36 years of age. He went two full years after that without fighting a single world beater, and only made two appearances in total, before finally entering the ring with Tyson in the summer of '88. He was ducking the best challengers, and showed up against Tyson without hardly a spark of interest in his eyes. Spinks had no desire to continue fighting after 1986 in my opinion. He was showing up for work to collect a paycheck, and that was when he even showed up at all. Frank Bruno, Tony Tucker, Tim Witherspoon and most of the top fighters of the late 80's would have been very difficult tests for a declining Spinks.
Spinks was a magnificent lightheavyweight - absolutely one of the best, ever. And while winning the heavyweight crown is something very few lightheavies have done and a fantastic achievement no matter the circumstances, i think as a heavyweight, Spinks wasn't all that. Remember that he should've lost to an aging but well prepared Holmes in the rematch. Blown away by Tyson easier than any other ranked opponent. Bruno was at the peak of his powers at 1988 and his robotic, based on size-style combined with top notch power, might be very hard for Spinks to overcome. If Michael is still in there by the 8th, then he has a decent shot (if it goes over 15) because Bruno's stamina has always been his weakness; perhaps more so than his chin. But otherwise, i see Bruno winning.
Bruno by ko tko, simply cos of the size and power advantage, and spinks didnt have the power or killer instinct to worry that suspect chin.
I am always a bit wary about judging a fighter to be shot based on a domination at the hands of an all time great unless their previous performence or subsequent performence were sub par. He might have been beaten by Larry Holmes in the rematch but then so was Ray Mercer almost a decade later. He might have been inactive but fighters have been inactive for longer and still come back. He might have been avoiding the best challengers but that dosn't necisarily mean that they would have beaten him. Gerry Cooney might have been shot in practice but a lot of people though that he was being handed the title on a plate. In short I don't think we know how far Spinkls had slipped.
As always hindsight has a lot to do with these types of discussions. I think even in late 88, after the Tyson defeat, most fans of the time would have Spinks winning..... Bruno always had demons against the very best, and going into 1988, despite Bruno coming off the Bugner win, both Tyson and Spinks rated above him. I do not doubt physically Spinks could of been in trouble, but as shown against another big man with problems with the mental side of the game (Cooney), Michael showed he could win. Spinks to overcome a fast Bruno start to win in about 12/13, as the pressure of the big fight once again costs The Bomber.
You make some good points, but I don't think a 1987 Cooney can be used as an accurate comparison to Frank Bruno. Cooney had only three bouts in 5 years, and hadn't beaten a decent fighter in more like 6 or 7. He was having on and off drug problems, was clearly not motivated against Spinks, and showed up at a career high weight. In fact, I'm almost even willing to bet that the Cooney who fought Foreman in 1990 was a tad better by virtue of his showing up in reasonable condition. Bruno in 1987 was far younger, in far better shape, and would not lay down against a top opponent. People question his mental toughness, but frankly I think he fronted some of the better losing efforts of the 80's.
If Bruno and Cooney had ever fought I think Bruno would have won. I think that Cooney would have been carrying his usual bagage and like Coetze he would have come in looking for an early knockout when in practice what he would have needed to do is take Frank into the later rounds. He would have brought the wrong fight plan. For all my criticisms of Bruno I think he is far more proven at world level than Cooney.