That's another problem, Q said they were just ONE of many races out there but everyone assumed they were the number one Galactic threat when they were never meant to be.
The fact that they were the only one Q brought them into contact with was the very reason that they became the number one threat to Alpha Quadrant forces. None of those other hypothetical threats were made aware of their existence as a potential victim.
Then they should've had some discussion about it at some point, something like "These Borg creatures were once considered out greatest threat. Nowadays we know that they're just one of many."
TNG should've just done the sensible thing and introduced other races as powerful or more powerful than the Borg after BOBW.