And this continues to be true of later Drones, despite our heroes learning that the Collective does interest itself in lifeforms and cultures.
It's simply a rare case of realism: when encountering a radically alien species, our heroes initially got most of the facts about them wrong. Humans could have been much older news to the Collective than the Hanson debacle, really, considering their low species number... Klingons, likewise.
Regarding assimilation and dilution of ideas: the Borg may originally have been quite serious about welcoming the distinctiveness of newly assimilated individuals and cultures. It's simply that this doctrine is doomed to fail when the Collective grows in size, and the Borg may not have taken that into account. Or then they simply saw that there was no way to take that into account, shrugged (it's one of the most impressive sights in this galaxy, really, sixteen trillion humanoids lifting their shoulders in unison!) and continued along the path set by their forefathers.