It is bannable, according to this tread: https://us.forums.blizzard.com/en/wow/t/sitting-on-a-flight-master-is-considered-zone-disruption/376525
This guy was bodyblocking the other facton’s flightmaster to trick players into clicking him, and Blizzard warned him it’s a banable offence. And that it falls under the same umbrella as attacking from a rooftop