The virus is a strategic mistake
The virus was released into the atmosphere, so unevenly and dependent on winds, the carnage will spread, quickly, but some survivalists, politicians, military, etc with bunkers with air filtration will get into their bunkers and wait it out. Not many, but there will be a few uninfected ready to come out 2 weeks later at full strength.
But let's look at the 7 billion unlucky ones. If you put the entire planet in an elimination match, 33 rounds later you've got a single winner. Some crazy angry guy can kill 33 people in 2 weeks easily, so we're down to one person left, right? No.
Not everyone will kill, hate need not inspire murder. Some will abduct and torture. Some will rape. Some will destroy property. Some will take a poo in your letterbox. But if you've got someone who deals with hate with murder, you're going to end up with lots of death around you.
Once I get the virus. I lose all fear and start attacking everyone I see. So I'll leave my home, kill my neighbours, and then.... there'll be no one left to kill. I'm not seeking trouble out beyond line of sight.
Each suburb / small town will have at least 1 person left standing. That person may not be the strongest, it will probably be either the person who was last infected (indoors, underground, scuba diving, etc) and so stayed clear of the gas, or the most isolated (out hiking, farmer out in the fields, etc) and stayed away from the melee for as long as possible.
The murder-fest is so sudden that your "post-apocolyptic"apocalyptic" world is extremely well stocked compared to typical fiction. Every kitchen cupboard has food in it. Every pharmacy still has painkillers and bandages. When the drop hits 2 weeks in, the survivors don't have to move far to sustain themselves.
They'll be really angry at each other for 2 weeks. Really tired for 2 weeks. And then they'll get real angry at those who released the virus.
Looking over a map of Australia and assuming 1 survivor from every small town, 1 survivor from each remote station, one survivor from each populated island, and one survivor from each suburb, the aliens will be fighting 15,000 pissed off people just on that continent.
Scaling that up to the entire planet I'd expect ~100,000 - 1,000,000 survivors. Each separated and unorganized, but reasonably well distributed around good landing sites, armed, accustomed to killing, and ready to pitchfork those weak aliens.
So what should they have done?
Use their knowledge to CUREcure an existing illness on earth. Covid19Covid-19 would seem to be a good choice, but cancer or heart disease are even better. The aliens are welcomed as herosheroes.
Include in the cure something really subtle. Say, reducing female libido around ovulation, or giving birth gives someone an eternal repulsion to sex (thus limiting families at a single child), or something else to reduce the human birth rate to less than 2 children per woman.
Eventually they get the planet, and we celebrate them as heroes the whole time they're slaughtering us.
