At least 800k Imperial Guardsmen got obliterated on Typhon, talking about dying for nothing

So I was playing DOW2:Retribution the other day, and the Planet Typhon(the death world with lots of jungles)'s information page, it is mentioned that the planet's currently got a population of 1.1 million. In the two previous games, it is mentioned that Typhon's only got some science stations and stuff on the planet, with a population of 300k. The information page also mentioned that the sharp increase in population is due to the immense Imperial Guard activity on it(Guards were sent there to deal with indigenous ork tribes as well as some leftover tyranids from the first Aurelian crusade).

So that's why Sgt Merrick lost his shi and whacked Castor in the head. When he talks about 'Thousands of guardsmen on the planet' I thought it's gonna be like a few thousand dudes from a couple regiments obliterated. But damn, at least 800k of guardsmen got blown to pieces? The Imperial's strategy is whack. There ain't even any efforts made to evacuate the valuable assests before the Exterminatus fleet arrive.

Also, I kinda feel like the Imperium's strategy in sub-sector Aurelia is a total disaster. They pratically sent a bunch of Guardsmen to Typhon which is a death world filled with orks and tyranids without ample support, effectively turning it into a Vietnam War in 41st Milleniumn. The guardsmen on that planet were so desperate and frustrated that some of them even defect to chaos cultists.(A renegade commander from Cadian 39th mentioned that since they were deadmen anyway, they would defect to cultists because 'at least they promised something in return'). On the ice planet Aurelia, the couple Guards regiment stationed there were under the influence of Ulkair, and most of them eventually descent into madness.