Seem, I always defended the game just based on "linear isnt bad", not really thinking about the reasons why its linear.
Ive also always been confused why FFX is well liked despite... also being very linear up until it opens up at the end? But XIII got memed for hallways???
I enjoyed 9 but similar to 8, at a certain point in the storyline in 9 I felt the story was done and stopped. (Spoiler) I defeated the evil queen and felt the story concluded enough and couldn't be drawn into playing the rest; it was hard to imagine what other threat could feel so personal after her defeat.
Similarly in 8, there was a point I can't recall at all where I felt the story was concluded enough and stopped.
Doesn't help that I hate missing stuff and google missable lists to avoid it and then keep on top of that; it's probably the reason I'm a huge fan of roguelikes.
it never really stops being an intensely personal story about loss, grief, and identity. there's a bit of a breather at the point you noted before the game begins to explore Zidane's personal history and the lengths some went to in order to survive death and the end of their world that they themselves caused. Brahne's personal ambitions were stoked into the flames of war by those who profited from it - who are these merchants of death and why do they seek the annihilation of the entire nations? Zidane's eventual crisis of identity on learning the truth ties the whole story together, narratively and thematically.