Their xenophobia was understandable.
They were alone.
Anything else, any other life-form, friend or foe, was outside the limits of their imagination.
The usual first contact routine.
Well, except that 8472 had explored all space and time, only to find that they were alone.
Until the Borg.
If they were alone... Why were they so well armed?
Humans in the real world are very well armed too, despite that we're alone as far as we know.
But you get my point.
8472 doesn't have a unified front.
What they did to the Borg, they must have already routinely done to themselves.
Why else have a pre-existing war machine?