But hasn't perfection, or something close to it always been behind the Borg's nature? "The Best of Both Worlds" I always took that episode title to be referring to the mix of natural and artificial (I realise other people have other interpretations)
What is it in BOBW Locutus says to Worf? "We want to raise the quality of life for all species." And in FC the Borg queen refers to either Data or Picard as "Imperfect."
The Borg, even in their earliest sightings, were all about harmony, a billion voices singing as one, the hive, symmetry.
I think it's easy to see some notion of perfection behind that. The only difference Voyager made to that was to suggest the Borg still strove towards some higher level of perfection, before this I think the perception was that they already felt they were perfect.