I think everybody understands that “cartel” is a figure of speech, useful shorthand. They are not the Sinoloa Cartel or the Tijuana cartel (who are, incidentally, now using drones to assassinate their enemies and mayors in Mexican cities and towns).
What there certainly is is an establishment of clubs who had been dominant for decades, and who most definitely did not want anyone to join their ranks, still less to become a dominant member of those ranks.
They are outraged by City, but they would have been outraged by Newcastle, Burnley, Crystal Palace or anyone else who aligned several years of being champions to their exclusion. It so happens that three members of that establishment wear red shirts when they're out on the pitch.