You are treating the term "war" too literally. This is not about some secret conspiracy, but the lack of incentives (or maybe even existence of disincentives) to support open protocols in the era of walled gardens.
To refute your last point, the article explicitly mentions that that Twitter has functional RSS support, which was deliberately removed from the user interface and metadata, so it's not a matter of development or maintenance cost.
English is a big toolbox. We don't need to repurpose words for completely different definitions. The suitably dramatic terms you're looking for are demise and downfall.
"The demise of RSS"
"The downfall of RSS"
Or if you want to get superdramatic: "The silent acquiescence of RSS to an untimely demise"
I actually agree thats dramatic, but its easy to see what they meant.
And no, not a downfall. A downfall does not convey the idea that measures were taken by other parties to actually bring down the entity in question. A downfall can be self-inflicted.
So not war, but not downfall either. :)
Just because one can puzzle out meaning doesn't mean that a piece is well written. It only means the reader was sufficiently clever, or lucky enough to stumble on the meaning.
Our experience teaches us that to have a war you need organized sides, no one can afford a war on drugs or a war on terrorism if the opponents can metamorphize into pleasure or the political will to self-determination.
Mechanical fish is right, RSS is unattractive to people, that is the problem. People don't hate it, it isn't a war.
pointing to a URL that already exists and works just fine doesn't cost anything. If the primary reason had been maintenance cost, they would have removed the feature itself.
The way to remove a feature gracefully is to first stop promoting it in any way, sometimes up to and including making the docs more obscure, because it's rude to urge people to use a feature on Day N and then rip it away from them on Day N+1. Particularly if some of those people are your business partners.
The next step, in many cases, is to send out sorrow-filled notices to the feature's users saying, in essence, that you're end-of-lifing the feature as of date X. Though often the bad news is artfully disguised. (e.g. "Look at all the glorious new stuff that we're rolling out to replace that tired old feature that will now be deprecated and slated for removal.")
Only in step three do you just shut it off. You might even shut it off gradually, as when Google shut off their old design for Gmail, a process which is still going on and appears to be taking literally years.
How much time elapses between the three steps depends on the details.
To refute your last point, the article explicitly mentions that that Twitter has functional RSS support, which was deliberately removed from the user interface and metadata, so it's not a matter of development or maintenance cost.