No, genius, it's statistics. Math. You know, the class you slept through in high school? I'll make it simple for you.
Out of 433 shooters:
12 were shot by randos (2.7%)
42 were subdued by randos (9.7%)
38+72= 110 killed themselves (25.4%)
If you want to be purely statistical about it, the murders were 10x more useful at stopping themselves than randos with guns. Which means that according to y'all's logic, the best way to stop a bad guy with a gun is to wait for him to stop himself.
I guess you could technically argue that the linked article promotes an anti-gun stance so it could be labelled propaganda (though I suspect you mean something more specific than just promoting a political stance).
However the graph itself is just the raw data displayed nicely so it's hard to argue that's propaganda or misleading. The graph is a little out of date but you can verify the current data by checking the source listed, the only thing that isn't displayed publicly on that page is the subdivision of the now 27 instances where a bystander shot the attacker. Edit: This does also include knife and gun violence, though.
Your assertion that more guns would make the results "vastly different" isn't based in any evidence, while the counter-argument that stronger gun controls and less gun-centric culture prevents mass shootings can be clearly demonstrated by simply looking at literally any other country. According to Wikipedia there have been only 45 mass shooting deaths (including attackers) in total in the UK this century. When a shooting happens here it's always newsworthy.