Here the core argument fails because it assumes ALL extraterrestrial civilizations would face identical technological limits and motivational constraints -- none would build detectable megastructures, none would colonize extensively, and none would maintain beacons. This is fundamentally inconsistent with the paper's own "Copernican mediocrity principle," which predicts significant diversity in civilizational trajectories, motivations, and capabilities; if even ONE exceptional civilization exists among potentially thousands, the "mundane" explanation collapses.
Really, all it takes is one exception to the rule. Just one. A species goes crazy and creates Berserkers, and there you are. (Is our own really THAT unlikely to do this? lol.)
And, despite how it's dressed up, the paper has nothing to do with physics. It's based on sociological priors (shared "lack of desire," boredom/fear,), and the conclusion is baked into the premise.
IMO even stuff like the Planetarium hypothesis is much more likely than this. In any case you must suspend disbelief.