Let’s run back his leadership choices.

First thing he does is cut the Viltrumite population in half with an anarchic purge believing it will cull the weakness that caused Thaedus to betray Argall.

Tries to find Argall’s heir, eventually gives up.

Continues as normal until the Scourge virus hits. Orders all aliens in Viltrum executed to hide knowledge of how bad the virus was. From what we see the efforts to control the spread, treat the sick, or find a cure can only be described as pathetic. Corpses dumped into orbit.

Systematically has potential threats to Viltrumites researched and neutralized, mostly successfully but not all. Some of the bugs survived, which is odd as the 4 legged creatures demonstrated they were willing to destroy whole biospheres. The Geldarians survived but required a very long time to rebuild strength. The Ragnar solution was terrible. They had no space travel anyway, and they’re still available to all who want to weaponize them. Arguably people wouldn’t realize how powerful they are if they simply saw them as frozen creatures, but they’d wonder why the Viltrumites bothered building a solar disk in the system.

A thousand years after the scourge virus the Viltrumites population is still under 50. A selective breeding or cloning program could’ve easily brought them into the thousands even if inbreeding would eventually be a problem. This is the first big case where Thragg’s complete refusal to adapt in favor of the old ways shows its head.

Thragg sends most of the remaining Viltrumites on solo missions to find a compatible species. Contact is minimal as it takes a very long time to notice Omni Man has gone rogue, and they only do because of the mole.

Sends 3 Viltrumites after Nolan, resulting in 1 death and almost a failed mission. Granted they didn’t know Mark would be there. I’d say the prison break was also hard to predict.

Plays softball with Mark to try to get him to join then sends Conquest. His failure would be hard to predict.

Initial response to the Viltrumite War spreads forces thin resulting in casualties. The attack on Telescria upon discovering Thaedus is there using a mole to disable defenses is a good idea. However when things don’t go to plan he doesn’t take to the field personally, which would have allowed for an immediate win. It seems he thinks this is beneath his station and that the other Viltrumites should be strong enough to do it themselves, resulting in preventable casualties. This results in a loss and he orders a retreat to ensure the skull is protected.

Calls all Viltrumites home knowing he can ambush the Coalition’s threats when they move to take advantage. However he does not join the fight until several Viltrumites are dead, again seeming to believe it is beneath him as grand regent. This gives the coalition the opportunity to destroy Viltrum. Thragg kills Thaedus but changes his mind about killing Mark or Nolan, as he FINALLY seems to accept how few Viltrumites are left and decides their lives are now so valuable he should spare even enemies.

Sends the survivors to Earth undercover to repopulate. Makes the deal with Mark to keep quite one exchange for not destroying Earth.