This... actually inspires very little confidence. The assassination of the archduke involved several assassins who each failed iteratively for ridiculous reasons on the motorcade route. Princip himself had decided to give up on the assassination, only to find out the cafe he had gone to ended up being directly on the motorcade path. The serendipity of his proximity was probably the only reason Ferdinand ended up dead that day.
The cannon doesn't have to work all the time, just once effectively, and possibly even accidentally.
The Merck attack seemed to be an accidental offshoot, and nothing on an international political scale happened from that. Until we have some more tech literate politicians, or an agency to explain what's happening in simpler terms, I don't see these kind of attacks being taken seriously, or even understood on a basic level.
In reality it was the setup of the triple entente by Edward VII that was most responsible for the WWs. The archduke may have been the match, but the triple entente was the detcord strung around Europe.
The cannon doesn't have to work all the time, just once effectively, and possibly even accidentally.