The entire thing with Viltrumites killing each other because Thragg wanted to get rid of their weakness doesn't makes that much sense if you consider that Argall was murdered by one of the arguably most powerful Viltrumites in existence, so really wouldn't it make more sense if they would try to kill all stronger people, logically speaking?
The Viltrumite empire really stopped working as a super villain faction when we actually learn more about it, since it's just a few evil empire cliches and tropes stitched together that anyone who is older than 12 should have already seen better executed in tons of other media.
Given how the Viltrumite population was so small by the time the show starts (less than 50 left) you'd think their Empire would have started to use good PR and offers of peace, stability, free tech, and food to get people to join willingly, as opposed to using brute force. Maybe the brute force approach would've worked well under Argall when they had legions of Viltrumites, but between Thragg's purge and Thaedus' virus, there's barely enough of them to run a banana republic, much less a galactic empire.
The closest thing I seem to remember where an evil empire weeds out the weak was with the Old Republic-era Sith Empire from Star Wars. But they themselves do not kill their own people en-masse like the Viltrumites did; they just had high training standards, and those Force-sensitive acolytes who fuck up in the training die. But if they pass the training, they're good to go. It doesn't matter to them whether or not an acolyte's strength in the Force is great or small, so long as they pass muster on the training and can kill shit, they're Sith. Sure, there's a few power struggles between some Sith here and there, but there's literally millions of Force-powered Sith in the Sith Empire, so the most that does is just change the name of the asshole that everyone bows to.
Even the bloody Saiyans did better as an evil empire, and 99% of them are literally a bunch of fucking low-IQ monkeys addicted to violence. Instead of weeding out the weak, they send out their weak and stupid as trash mobs to take enemy planets, for them to sell to Freeza. Either the weak die off and they have less mouths to feed, or the weak succeed and the Saiyan Kingdom makes money from their exploits. Someone like Bardock, Goku's dad, was born as a lower-class weakling, but thanks to his many battles, he grew stronger to the point where he was almost as strong as King Vegeta. So at least the Saiyans give their weaklings the chance to grind and get better; the Saiyans don't just toss 'em aside.
Even when they had a total wimp like Goku/Kakarot who was born with a pathetic power level, he eventually grew to be powerful because of training. If Thragg was the king of the Saiyans at that point, Kakarot would've probably been euthanized in the crib, and the Saiyans would've never been able to beat Freeza as a result.
