The problem is whats being perfected. The Borg drones or the Borg Collective. They are two different things.
The Collective is seeking perfection, and sends it drones out to pursue those goals.
Drones are simply parts of the collective. If the collective were destroyed, those parts are no longer Borg, because they never were.
perfection of the parts = perfection of the whole. looking at their omega molecule fascination is enough to establish that. molecule does not exist in it's perfect state without it's parts being so as well. so perfecting the drones IS part of perfecting the collective.
One thing I have never understood about the borg is their use of time travel. They don't seem to be constrained by a "temporal prime directive" or whatever it is called. So if I were the borg, ever few decades or so, I'd send a ship back in time to give technology from the future to the past. This would also give decades worth of knowledge and exploration, insight into various battle techniques, and myriad other advantages to the borg of the past to exploit.
So why don't they use time travel to help themselves?
i wonder the same thing. same goes for that transwarp conduit. so much potential to get what they want yet they don't use it fully. they never use anything they have to their full advantage, aka inefficient which means they are going against their directive/goals.