Lemme fix that FFX Sphere Grid image for you:
(People say they're the same because superficially they both have an extremely linear gameplay path, limited exploration in each aside)
Europeans (and JP International Version) had the expert grid which gave you much more customization than the standard grid.
The HD version includes the Expert Grid too.
I personally think the games are much closer than some are passing off here.
My opinions below
* Both games are hand holdy and easy until the latter parts.
Yeah, I agree.
* Both have large expansive landmasses where the end-game content is.
But FFX has more than the Calm Plain. You have the post-game areas you discover with the ship, there are optionable summons, and more diversity of sidequests.
* Both upgrade systems push you towards certain roles for the characters. You have to grind hard to create your own roles.
The Standard Grid, probably. I've only played that game with the Expert Grid though. That gives you much more freedom. Crossing paths was really, really easy. There are less slots for the getting 255 in every stat part, but the flexibility is much better.
* Majority of FFX is walking straight in linear dungeons just like FFXIII. But it still has towns, just about.
True. But as the OP said: A) Is masked. B) There are more and more interesting sideways.
I say A because you have stuff like towns and temples (which have puzzles) and there are more areas where you can wander around and find some special weapons / special summons / sidequests and other contents. I won't give you clear examples because I've played the game in Spanish so it's hard to me to name you a few. If you can't think of those examples I'd try to make the effort
* Racism towards Al-Bheds = racism towards L'Cie/People from Pulse.
Racism is a really common cliche in JRPGs. Not limited to FF.
* My Dad is a whale VS My Sister is a crystal.
I think the idea is different. The Dad part is a plot twist around the end of the game. The sister part is supposed to be Lightning and Snow motivation at the start of the game (well, outside them becoming crystals too).
* Sin destroys world VS L'Cie destroys world.
Monster destroys the world is another JRPG cliche. Not limited to FF neither.
* Corrupt leadership/pope-like figures.
That's another JRPG common theme.
FFX is better, but it already had signs of the direction the series was heading.
I agree with this conclusion even if I don't with some of your points. Final Fantasy XIII looks like the saw the success of FFX, decided to make a similar game but only scratched the surface instead of analyzing, what it did well and what it didn't.
I find in some ways FFXIII it's almost a caricature of FFX. You have the same flaws, but they're even worse. And you have many stuff that is quite similar in the surface, but when you try to go deeper you can't in FFXIII while you certainly can in X.