Premises establish only that newspapers can’t cover all sides of every story. (Some stories won’t be adequately covered.) The author thought this implies newspapers can’t cover all sides of any story. (Every story, including all important ones, will not be adequately covered.)

This possibility doesn’t hurt the argument, because the author never concludes that having 2 newspapers is sufficient to see all sides of important stories. Having only 1 isn’t enough. But the author never said having 2 is enough.

The conclusion is not about what newspapers should do. It’s about what people (”everyone”) should have access to. Also, one of the premises asserts that all sides of an important story “should” be covered. So the premises are not just factual statements about what newspapers do.

The author doesn’t assume that everyone can access all newspapers. What people “should” be able to access is separate from what they in fact can access.

There’s nothing flawed about making an argument focused only on important stories. What matters is whether the premises prove the conclusion. The choice of what kind of story to focus on in the argument is not itself a flaw.