One thing the Borg have going for them is sheer numbers to overwhelm a whole planet. They don't need to precisely destroy anything as destruction is not their agenda. If they rely on numbers they will be weaker when they don't have those numbers available. The Borg "fleet" seen in VOY was very impressive, but these numbers are in the DQ not the AQ. Yet.
The Borg could overwhelm the entire Federation if they wanted to.
The writers should have emphasized that the Collective was 'toying' with the Feds constantly, using them to promote technologies against them, and could have staged the entire Endgame fiasco as a ploy to determine just what methods humanity uses and the process behind those methods (or way of thinking so they can better adapt).
Essentially use them as lab-rats of sorts.
Eliminate the queen too.