Oh boy, the ever popular "the series is going downhill" thing. I have frequently said & still maintain that it is too early to tell. We haven't had many main series games since IX, which most people thought were pretty good. We've had a bunch of spin-offs, but...meh.
In particular focus to the spinoffs, I don't mind if it's "milking" because they're...good. Compilation, anyway. Ivalice Alliance can suck my left nut. You can say what you want about the Compilation, but it's clear that they're still trying. Hit-or-miss, the materia, materia fusion, shop, & DMW elements of Crisis Core were all pretty finely tuned versions of gameplay elements that we've seen before. The DMW even had some really neat scenes where it tied into the story, such as Zack's death.
Dissidia, while not a Compilation game, also did its fair share of tweaking. The Brave System, again kind of hit-or-miss, was a pretty unique element for a fighting game. If nothing else, it DID successfully turn the game from "button mashing combos" to "you may actually have to plan a little."
In terms of writing, yes, I would say that the series is very well-written at its height. Maybe not well translated, but that's something different entirely. But the question is kind of unfair, you know? What are we comparing it to?
EDIT: TWELVE is "good writing"? SERIOUSLY?
As to what he's saying, he's commenting that some story elements aren't put together well, giving you sort of an "emotional whiplash." While I don't agree, especially considering the specific example is nearly an entire disc apart, he's not saying that Aerith's death was a shitty plot element.