I can see a use case where devs who don’t feel like building for Twitter’s API will want to use RSS to quickly get a user’s recent tweets. But I don’t think this will significantly impact anybody’s anything, and it feels like the author is exaggerating the consequences.
Most users of anything don't care about RSS. Most users also don't explicitly care about the API, either — those are both at a lower level than what users notice. That doesn't mean they're worthless.
I can see a use case where devs who don’t feel like building for Twitter’s API will want to use RSS to quickly get a user’s recent tweets. But I don’t think this will significantly impact anybody’s anything, and it feels like the author is exaggerating the consequences.