So it's interesting, feasible, but it's probably not as broad impact as the scariest scenario leads out to be.
Also I imagine that once exposed it becomes a well known pattern. Some will still fall from it but I imagine once it's been done few times it becomes even costlier.
The fact that Xz is mentioned and most of us know right away what it means show that we collectively learn.
Fake news always existed. Now one dude in India can flood multiple sock puppet media accounts with right wing content/images (actual example) at a scale previously unimaginable. Same goes for social engineering tactics.
To use your analogy: this is much like a forest fire. Tinder-dry combustible stuff is piled up everywhere, there's no lack of ignition sources, and firefighters are thin on the ground.
Fun times ahead.
Only mentioning that it feasible or even has been done few times mean that people who care will act accordingly. It doesn't remove the problem but it makes it radically less effective already by just being aware of it.