That one trick would have been fine, if they had stayed as apparently unstoppable as they were in Q Who and the BoBW two-parter.
The introduction of a Queen basically made them 'stoppable'.

When the D first encountered the Borg, Deanna made a good observation about the Borg:
"TROI: We're not dealing with an individual mind. They don't have a single leader. It's the collective minds of all of them.
PICARD: That would have definite advantages.
TROI: Yes, A single leader can make mistakes. It's far less likely in the combined whole."
Introduce a single leader (aka as the Queen was in First Contact), and the Borg are suddenly prone to losing much more effectively.
Also, Picard having flashbacks of the Queen dating back to his assimilation could have been implanted by the Borg. He was able to 'sense' them... whatever mechanism allows for that, would likely give the Borg ability to transmit images to his brain.
The Borg should go back to existing without a Queen (which could be described as an 'experiment' the Borg Collective decided to abandon when Voyager destroyed the TransWarp hub).
And 7's and Picard's knowledge of the Queen would have been implanted by the Collective of sorts to make them think she always existed (well actually, even 7 did ask the Queen a question as to who was she in Dark Frontier - when 7 should technically know that).
To me, this points to the premise the Queen could have been a temporary (but intentional) existence on the part of the Collective.
At the very least, the writers can easily write the Queen's existence using this premise.