I tend to think something like Game of Thrones resists easily devising a storyform because in a lot of ways it's not one story (with the possible exception of season 1 which really did feel like it was condensed down to Ned Stark's story.) But in most seasons you could just extract one of the POV characters and find a pretty clear OS, MC, IC, and RS just for them. Think of one of the middle seasons where Jayme Lannister loses his hand and spends most of the season with Brienne. That story is so vastly different from the one Jon was dealing with north of the wall. The same is true of Dannyeris in Essos and probably of Arya as well. This isn't the case every season, of course, because as I recall in the subsequent season Jayme was just a part of someone else's story.
Warning: season 8 spoilers from here on . . .
The problem with season 8 for me is precisely that it does collapse down into a single storyform. Jon Snow is the MC (in the situation of being the true king but not wanting to be), Dany is the IC (with the fixed attitude that she must be queen no matter what), the OS is in the activities of fighting for power and the MC in manipulation as the lovers fall apart because of their incompatible natures. On the MC/IC axis, Dany's all about "the ends justify the means", Jon refuses until the finale to do what everyone keeps telling him he needs to do, and finally changes to her position when he kills her.
So maybe what makes season 6 unsatisfying for viewers is that they'd grown accustomed to a multi-storyform show that always felt richer and more complex and in the end were given a pretty bog-standard final season that's just about a guy who should've taken the throne but didn't want to pay the price of being king. The story goal was to save the seven kingdoms (which they did), but it turned out bad for Jon (who asks at the end if he'll ever know if what he did was right). Though you could argue the epilogue removes some of his angst.