I can forgive the weakened state of the Sphere, Worf had said shields were down on the E-E so its possible this happened to the Sphere, without shields to stop the Q-Torps there was no way to adapt until it was too late.
I always assumed Borg shields acted as a scanner when they were hit by a P-Torp or Phaser to find the frequency/modulation of the weapon so it could adjust.
It would be similar to if I were fighting Mike Tyson and I had personal shields, the first few punches/bites would allow me to get a good idea where he plans to strike and adjust my game plan.
If my personal shields were down then id be sleeping after the first punch...
... I have no idea where that analogy came from.