Farming is the entirety of Warframe's "content"

No it isn't. I have no idea why you and the many others like you endlessly parrot this crap.

The actual content of the game (other than exploring tile sets for the first time when you're new, and quests/raids) is in modding and customizing Warframes and weapons and, essentially, having fun experimenting with a variety of setups and strategies while blasting baddies. Attempting challenging endless missions/nightmare raids is another sort of content.

The grind and platinum are gateways to getting something new and cool to try or show off. You pay with either time, money, or both; we all know this. That isn't "content," though.

Then again, maybe there's a legion of brainless drones out there for whom repeating the same task endlessly in and of itself qualifies as "content."

Of course it's not a coincidence. If they're going to be working on a frame (even for a skin), they might as well re-examine the entire thing. It's not as if DE only introduces reworks when they can find ways to monetize it, they just happen to throw aesthetic changes in with mechanical ones.

That may be, but they pulled a twofer this time around. When a frame has been really bad for a very long time, not bothering to rework it until you're vaulting it is obnoxious.

Vaulting isn't a new skin, or "taking a look" at Ember; they're simply removing her parts from the drop table. Waiting until the vaulting was announced to finally give Ember the buff people have been requesting for ages has compelled newer players and casuals to scramble for a set, and therefore of course driven plat sales.

You're free to justify it however you like.