The thing is, the reason the Borg in FC were assimilating the crew was because their cube had been destroyed, there were only a handful of them, and they needed to replenish their numbers. The mistake Voyager made was assuming that assimilation was the norm rather than an exception. VGR even made the bizarre claim that the Borg don't reproduce, only assimilate -- which doesn't make any sense. How can they add a species' biological distinctiveness to their own if all their drones of that species die out in a single lifetime and aren't replaced? Not to mention that relying entirely on assimilation would be too inefficient and slow a method of building or maintaining their numbers, the same way that a hunter-gatherer subsistence is far less able to sustain a large population than agriculture is.
Hypothetical, if the remenants of "The Borg" gain the Genetic Engineering & Cloning Tech that the Founders had for manufacturing in large scale of "Jem Hadar". Let's assume that "The Borg Queen" that JLP destroyed in ST:PIC wasn't "The Last Borg Queen", but there was another one out in the Delta/Gamma Quadrant trying to attain Founder Tech and they manage to do it.
How terrifying would a army of "Jem Hadar Borgs" be with "Individuality", but genetically & technologically enforced loyalty/devotion to "The Collective", especially given the Clone/Birth/Growth rate of Jem Hadar along with their quick learning capability and "The Borg's" technological might? One that didn't need "Ketra Cel White" anymore.