Look, whatever Tommy Trotter thought about the two horses in the fall of the 1979 campaign has no relevance to how good "Bid" became as a 4-year old, which was his best season. And if you are going to compare horses, best-season-to-best-season is the only fair way to do it. So that means the fair comparison is Affirmed as a 4-year old vs. "Bid" as a 4-year old, not Affirmed as a 4-year old vs. "Bid" as a 3-year old. And the numbers are irrefutable - "Bid"'s 4-year old season was better than Affirmed's 4-year old season. The fact that Affirmed at his peak beat a Spectacular Bid who had not yet reached his peak has little to do with who the better horse was.
You seem to be arguing against the idea that horses usually improve as racers as they mature. And almost any horseman would tell you that 3-year old thoroughbreds are not as physically mature as 4-year old thoroughbreds. So, what is so radical about the idea that the 3-year old "Bid" was not quite as good as Affirmed's best, but that with another season of maturity and improvement, 4-year old "Bid" became a bit better than 4-year old Affirmed had been?
And about your 75% figure, that may be true across all classes of thoroughbred racers, but it is not true at the championship level, which is the one being discussed in an Affirmed vs. "Bid" discussion.
