It's a problem, but if you can't understand how it'd be less of a concern than shootings like this I don't know what to tell you.It's really morbid how gun nuts don't even try to say this stuff isn't a problem, and think the problem is that shootings with 4+ victims shouldn't be classified as "mass shootings".
Also criminals will shoot other criminals, here in Denmark the vast majority (probably like 99%) of all shootings are committed by criminals with illegal firearms that were never registered in the first place.