Even with advanced tech, a global population of 9 billion feels crowded if everyone expects a first world standard of living. Even 2.5 billion might feel a bit crowded.
If I were the aliens, I’d just culture some more of the deadly virus from the lung tissue of the corpses on the mall shuttle bus or from the infected Russians who were on the Irina Bogdovnof. This time, I’d continuously release bits of the virus as I incubate more. Once the genie is out of the bottle, it can’t be contained anyway, so who cares how it’s released?
Or I’d use my teleporter to insta-swap the planetary populations. If feeling merciful, put the Earthlings on the alien planet. Otherwise beam them onto the moon or into deep space.
It’d be interesting if the creators of cancelled scfi dramas like these, after getting an early cancellation, continue the story at least in paperback form.
The original form of the virus worked too well- it’s incubation period was next to zero, so it burned out before it could spread widely (utterly impossible irl, but hey..)
Re. having enough room, it’s not the carrying capacity of the planet, it’s cultural and political conflict. Think Israel/Palestine multiplied by a thousand.