> the final series of game of thrones retroactively killed the cultural phenomenon that it was

I agree with you on the observation. Subjectively I feel the same. I wonder if someone has hard data on this. I wonder if there is some executive somewhere looking at a graph of polling results, or merchandise sales or anything like that and feeling terrible that they have screwed up (at least privately, even if they would never admit publicly).

I believe that the latest few seasons removed from my enjoyment of the whole franchise. It even made the earlier episodes worse, in the same way a flat punch line ruins even the most masterfull lead up of a joke. But does this feeling also appear on the bean counting level? Fundamentally a franchise is a business enterprise with the goal of making money for the owners. Does “ruining” a series this way also effects the bottom line in a way which can be expressed in the accounting?

That's actually a good example - The early seasons aren't necessarily worse because of the end of the show, but it definitely killed a few spinoff shows HBO was planning, and also killed the Star Wars movie that the showrunners were working on.

Obviously we're still getting House of the Dragon, but if you'd told me before the last season came out that we'd only have 1 spinoff GoT show now, and that it wasn't that big of a deal, I'm not sure I'd have believed you.