Theory of Flightless Birds Shot Down

I dont think that these guys have considered that genetics doesnt "Determine evolutionary pathways" it merely records the changes. Besides, epigenetic variation hasnt been considered. Scoby ducks , pekin ducks, Indian runners, and mallards have virtually similr genetic makeup, yet only mallards fly. AND, they all are variants of one mother duck(er)

How do you shoot down a flightless bird?

I woud not

I think that this is an example of overenthusiastic science reporting. There are several facts that dont hang with the "shot down" position.
The fact that Ratites all originate from those islands and continents which are in the chain of the breakup of Gondwana, and the fact that they DO have their major genic complements arranged in a kind of geographic order, to me, suggests that the founder population of flying birds had successfully migrated to the splitting islands and continents and evolved from a common rootstock with convergence as an evolutionary adaptation. Remember, the thing that ws common to the SOuthern Hemisphere was that it took several tens of millions of years to evolve newer terminal carnivores so the entire southern hemisphere was "open" for colonization.