That was part of my point, yes. But I still stand by my statement that the Adeptus Astartes are as much the genuine creation of Games Workshop as anything is anyones genuine creation. When creating a futuristic elite military force you have to borrow from the concept of elite military forces itself, but that doesn't mean the creation is simply a copy of something else. The names are "stolen", yes, but that's because the 40K world is a darkly futuristic version of our own.
When stripping away the superficial things like "elite military force" and "warrior monks" from the Space Marine identity you are still left with a very detailed, interesting and darkly gothic history of genetically engineered futuristic warriors not wholly human who defend something not really worth saving (the Imperium). The concept is quite unique to Games Workshop in that similar concepts in the fantasy/sci-fi genre are not easily identifiable, unlike elves, dwarves, orcs, lizardmen, monsterous aliens, elves-in-space, human empires, chivalric knights and killer robots. That in my opinion is why Games Workshop spends more time and energy on Space Marines than everything else related to 40K combined. The Space Marines are their baby and noone elses.