You're comparing three modern BoPs attacking an Enterprise that has to stay in one place (it's protecting the E-C) to one non-modern BoP attacking an Enterprise that has options in terms of maneuverability.
Additionally I believe the BoPs in "Yesterday's Enterprise" are considered the larger class, while I'm pretty sure the BoP in Generations
is not meant to be that class.
In any case, the E-D could have rotated shield frequencies (randomly), it could have actually used all of its weapon systems, it could have gotten the hell out of orbit. The ship withstood prolonged attack by a Borg cube, but one old BoP takes it out? I don't buy it.