There's a huge difference though. Chapter 2 of MGSV was a lot of repeated missions with a half-baked (if that) story in the middle. It also had no real conclusion. The "linear" stuff in FFXV doesn't sound like that at all, nor does it sound like the game doesn't have a proper climax/finale. It sounds like the "openness" begins to pare down in the second half to focus on the plot more, with only the last stretch or so being in a dungeon or dungeon-like environment which is typical of most RPG's.
This doesn't sound like an MGSV case at all. Sure, that choice for them to go more narrative instead of making the open world even more open...er could be because of budget/time, but it doesn't say that the entire second half of the game is linear weirdness.
MGSAV lacking a climax was the least of its problems.
I'm in the camp of people that thinks that, a proper Episode 51, would've changed little to nothing about my opinion of the game.
By the end of it, you could see more than clearly through its facade (as much as i loved to death its gameplay).
I don't expect FFXV to be anything of that magnitude, but i'm wondering if it didn't run into a similar problem, with over ambition.
After all, having a massive open world game with that level of polish, isn't something you see often (almost never, actually), it wouldn't surprise me if they decided to tone back the second half, in terms of scope, for that reason.
But again, as long as it works in context, i wouldn't be mad.