Could the Ali of Spinks 2 have done anything to Holmes?

No.
Leon Spinks is probably the worst lineal HW champion in history.
In 1978 Holmes would defeat Ali (Spinks 2 fight) by unanimous decision, but more convincingly than he defeated Norton.
Holmes is "hungry".
There is a huge difference in the quality of Leon Spinks and Larry Holmes.

 

Just to add I think a prime Ali would win a decision over Holmes but the version of Ali vs Spinks more than likely Holmes would beat both Ali and Spinks on the same night that's how far gone Ali was.

Shavers did alot of damage to Ali and that was the real start of the downfall in regards Ali's parkinsons.

 

No. Muhammad had regressed too far by 1978 to beat a prime Hoimes. It would n't have been the horrorshow that their 1980 bout was,though.

Holmes by clear UD.