I rooted for the comet too but I laughed a lot and loved the movie. It didn’t strike me as “smug” because it skewered the POV scientists (Mindy’s susceptibility to the spoils of sudden fame, his wife outing him as an overgrown child, and Dibiasky’s moral indignation over being forced to pay for free snacks) as much as it did the President (no political party mentioned, IIRC, and parallels could be drawn to either one). It was spot on in poking fun at vapid talk shows, celebrity worship, memes standing in for intellectual discourse, and naked political and capitalist opportunism. It skewered the adulation of obscenely rich tech moguls who play at saviorhood while trashing the planet with one foot in their intergalactic escape pods.
What the movie’s metaphor gets right is that the disaster could be stopped if only the powerful could see past their own greed.

You’ve identified that a comet is an imperfect metaphor for the climate disaster or pandemic because “no one is to blame” for a comet. But this satire would be decidedly unfunny if it existed only to litigate who is to blame for the global disasters at hand. If you were looking for a satirical film to provide a clear verdict or an actionable lesson, it’s easy to see why Don’t Look Up left you unsatisfied.