It doesn't seem like the FEE article citing CPRC and the NPR article disagree very much. But it's true that some people will trust the NPR one much more, so that's valuable.
Edit: I mean, the numbers in the articles aren't necessarily the same, but the idea that the US could be better and could be worse is present in both.
I do live in the US, and there's never been a mass shooting where I live, either. The US is a very large place. Things vary quite a bit from place to place. A shooting totally could happen near me, I'm just saying the size of the US and its large population does make them look like a more common thing than they actually are sometimes.
I agree that public indiscriminate mass shooters probably are not deterred by the thought of someone else having a gun and shooting them to stop them. In fact that may be what they want a lot of times. Public mass shootings are a very small portion of gun deaths, though, even in the US. There are some lists of shootings that include things that don't really belong. Gang violence is the one most often cited, if 3 people from one gang and 2 from another shoot at each other over a dispute, that's technically a mass shooting by many definitions, even though its not really contributing to anyone else's safety.