It doesn't feel right sticking up for an IMGer, but I'm afraid it's got to be done...
1. I vaguely remember Ross's book on the Tories and, IIRC, it contained no claim that the Tories were bound to lose the next election or anything of the sort. I think Ross pointed out two
long-term declines in the Tory Party: (i) outside England and (ii) in large sections of the middle class.
He was right, wasn't he? The Tories are not a major party outside England and large sections of the middle class have abandoned them. Believe it or not, back in the 60s it was normal for teachers to be Tories! The middle class was overwhelmingly Tory.
Ross and others also pointed out the very high average age of members of the Tory Party. Though they have tried, AFAIK, they have not overcome this problem much. If they don't, the result is obvious: they'll die off.
The Tories have been doing badly in the polls for almost all of the last decade and more.
2. At the time, I had no sympathy for the Sparts' slogan (which you suggest Ross pretty much agreed with), but the Sparts turned out to be highly prescient about Afghanistan. It was the Sparts who pointed out what the consequences would be of the Communists being defeated by the Islamist rebels in Afghanistan: civil war between Islamist factions and then a regime that would make the Iranian theocracy look almost mild.
And lo it came to pass. If only the PDPA and their Soviet allies/masters could have won!