The "myth" that every first world country has criminals? (doubt) Or the "myth" that this stuff doesn't happen a lot in other first world countries. Get off the fanfic internet and onto the data sites, please.
This graph is from the Rockefeller Institute of Government. https://rockinst.org/blog/public-mass-shootings-around-the-world-prevalence-context-and-prevention/ By a less narrow definition of mass shootings, i.e., "a minimum of four victims shot, either injured or killed, not including any shooter who may also have been killed or injured in the incident," the Gun Violence Archive (with an actual indexed archive of events to back it up) counts between 270 and 690 mass shootings by year every year since 2014. https://www.gunviolencearchive.org/
And, yes, they have a political angle: they don't like seeing Americans die senselessly. But they're gathering data, not manufacturing it.