My problem with the sphere grid is that I don't see the point to it. If you're going to have us follow a strict path until end game, what the fuck is the point? I like my characters to have roles as well, but FFX takes this to an extreme by making the roles too niche. The dog is ALWAYS for Tidus. The armored thing is ALWAYS for Auron. The flan is ALWAYS for Lulu.
FFIV and IX offer more variety in enemy encounters, and more interesting sub systems. If FFX didn't have a sphere grid, it'd still be the same result. Tidus would learn cheer with or without a sphere grid. The difference is, without the grid, you'd have to actually put EFFORT into your shop purchases rather than just click learn skill in the sphere grid.
FFVI and VII, characters are not wholly interchangeable, especially VI. The same is true for XII, and especially if we're talking about the International version. On the other hand, it's possible to make all the characters the same in X, so I'm not understanding why you defend the grid.
I like XII's grid more. When I play XII, I pick a strict path for guys to go, and I give each character a role that I create myself. Since Ashe is my mage, I'm not going to put her down the weapon path or the attack power path. I'm going to put her specifically on the path to learn new magick and wear light armor. I really like how XII allows you to do what the fuck ever, at any point in the game. I feel the same way about V and VIII. My favorites in the series are the ones that let you do anything, in your own way, in your own pace: XII, VIII, 1, V, VI, and X-2. I think IV and IX are the exceptions to the rule for me, as I highly regard them despite their linear character progression.