So, if we assume that Ancients were colonising the galaxy with subluminal methods en masse, and only discovered subspace during the process, there might be some interesting thoughts to make. For example, Ancients may have tried to expand into a different galaxy/star cluster via subspace and alerted Shivans to their presence - and the steamroll had begun. And while the parts of Ancient empire that actively used subspace for travel have been eradicated, the ones who didn't invent subspace FTL methods "yet" had to be eradicated by Shivans with more crude methods. If there's a populated system that no nodes lead to, or they're too unstable for even Shivans to travel, or there is a some kind of Ancient colony ship traveling through the void between systems, I guess Shivans might have taken the approach of totally spreading throughout the galaxy and methodically eradicating whatever remains they can find. Maybe the Lucifer armada was going around doing just that, yes, it might have taken them 8000 years after the subspace part of the empire fell, and they got... attracted by the sudden increase in subspace activity with the T-V conflict erupting.
Also, I don't see how Lucy could survive such a strike, and several dozen tonnes of metal accelerated to near-c speeds is by no means a conventional attack... Looking up some relativistic energy calculator, it seems like a ton of stuff accelerated to 0.9c gives you over 100 exajoules... I'd call that a planet-cracker. Even if Lucy's shields managed to absorb the hit, I really doubt the resulting acceleration wouldn't instantly make her break apart. Of course, we would need to know how the shields exactly work to make the jugdement.
My guess is, based on how the ML-16 works against shields of Shivan fighters in FS1 and how Maxim does that in FS2, that while shields are potent in deflecting/absorbing mass accelerator shots, they also have their limits. The fact that a Shivan bomber can regenerate its shields faster than you can spam ML-16 bolts at it doesn't mean that ten thousand of these impacting at once would not instantly evaporate it, or that a sufficient amount of Fury warheads doesn't do the same. Actually, isn't Avenger a weapon based on bullets?
And if we compare the biggest capship guns or warheads attacking Lucy to these pitiful ML-16 bolts bouncing off of a bomber, wouldn't a big enough impact also kill it?
And uhhhh, beams are basically a kinetic weapon too. Yet they penetrate shields, maybe because fighter's systems don't have the time to react to them? In this case, fastas**** object don't really differ much.