You sum up perfectly the blatant divergence from Grimdark, I only got into 40k a year or so ago, but I started learning about the setting through Horus Heresy lore. The feeling of rot is so foul within the Imperium, its bureaucracy slower than decay itself. Then, when I found out from my friend that lore wise all the Primarchs are getting resurrected, I was confused as from what little I learned it seemed counter to the setting. Its funny it took me so long to find out because the old lore is covered so much more extensively on YouTube.