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???
Because FFX is good and FFXIII isn't, simple as that. 13 is like 10 but worse in every single way. The characters aren't as interesting or fleshed out, the overall story isn't as personal or understandable. By the end of FFX you know exactly what the world looks like and why everyone behaved the way they did. By the end of FFXIII you need to look up "ok so wait, what the fuck was I even doing this whole time?"
Gonna disagree about XIII's characters, though not necessarily the overall plot. I love XIII's main cast and think it has fantastic character dev though. Its actually the game's main strength imho.
I mean yeah the characters are its strongest feature, but they're all still significantly weaker than FFX's characters. They're very similar games. That's why it stands out so much when it doesn't reach the same heights. If FFX never existed FFXIII would be widely beloved.