MK wrote lore to make Cyrodiil correct lore wise, so it's ok.
The lore might justify the way Cyrodiil is now, but it doesn't change the fact that it resulted in Cyrodiil being a more boring and generic place then it could have been. And if the designers had respected the original lore to begin with, there would be no need to write new lore to explain the change.
I think there really is no more evidence we could possibly need to put our fears at rest about a bland culture in the next TES.
I can't say it really satisfies me, after all, it's easy to
say you're going to do something, now actually doing what you say you're going to do is harder. I'll believe said promises when Bethesda shows clear evidence that they're making an effort to build a much more interesting setting for any future Elder Scrolls games. As much as I'd like to think that Bethesda learned their lesson and realized that they had the right idea with making Morrowind a unique setting, it's a bit too early for me to be willing to count on this simply based on a few words.
Maybe a god did change it. Maybe it's never been any different, but a handful of religious scholars changed history one day by writing that Cyrodiil used to be rainforest and jungle until a god changed it to suit man's desires. Therefore, we should all worship the gods, because they have shown their love for us with the metamorphosis of Cyrodiil into a more hospitable climate!
But that's not what the lore says at all, and fiction should be able to be interesting on its own based on what it tells you. If you need to come up with your own, unfounded, theories about some aspect of a work of fiction to make it interesting, then there's a big problem. And besides, whatever the explanation, it still doesn't change the fact that Cyrodiil would probably have been much more interesting as a jungle than as what we got in Oblivion.