I disagree. The Terran marines face some pretty scary stuff. Everything they face can easily shrug off hypersonic-railgun rounds, for starters, and they go against them with even less numbers then the Imperial Guard. It's really "doing roughly the same with even less."
The stormtroopers, on the other hand, fall victim to the bane of bad guys everywhere: being the antagonists in a Hollywood production. Few can escape from such a terrible curse.