But thats the thing though. Why did they feel the need to retcon the Thor fight as being a clone?
With Thor's history, and what he unleashed in their encounter, was it unbelievable to just let Thanos loose that one?
At some point it just becomes ridiculous to protect a character fight record like that. That the writer of the Squirrel girl story thought necessary (and funny) to include a Watcher to certify it was *THE* Thanos says a lot about the level of protectionism in the air. It was almost like they needed to laught at it a bit.
But you do keep saying that Thanos has suffered multiple humiliating losses that have been retconned. What losses are you referring to? If the Thor loss is understandable under the circumstances, then it is not humiliating. So you have Ka-Zar and Squirrel Girl, which is only two and Starlin had nothing to do with Squirrel Girl. Thus, that leaves only Ka-Zar for him.
In 1992, Starlin had Thanos give up his nihilism and has continued to write him as NOT being nihilistic to this very day. In 2000, Starlin wrote Infinity Abyss whose story is based on Thanos seeking to stop a group of his clones who inherited his past nihilistic ways from destroying the universe. With such a plot, it does make sense to explain why between 1992 and 2000, we have seen at least three times when Thanos is trying to destroy the universe. The notion that Starlin did this stricktly to undo the losses is an assumption.