Voyager didn't weaken the BORG... BOBW's did the minute Picard said the word..."Sleep".
That weakness was compounded when the Borg never sent a followup cube with its sleep function disabled to whip the Federation's collective backside.
There's canon and then there's just story development
... kind of like how Superman could "Leap tall buildings in a single bound" before his creators realized it was cooler if he could just fly.
Like how TNG's Trill love story with Dr Crusher was "sad" because she couldn't accept her Trill male lover in a female host body, but by DS9 the Trill love story was sad because the Female Dax and the female scientist couldn't get together because associations with former lovers was taboo.
I like to cut our writers a little slack.