Energy shielding is one of the Domain of Man's greatest achievements in military technology. Blackrock has basically reverse-engineered their way up to par, but cannot figure out how to make efficient shields, so they have to rely on their efficient powerplants, engines and weapons.
It's the same with the phase cloak and phase systems - a lot of weird weapons came out of trying to replicate the underlying tech behind a phase cloak, like the Shard, the AM Lance, and finally the Scalar Deracinator. Now that they have phase cloaks working, it still doesn't work quite the same way as it does on Domain vessels, but Blackrock has designed around it.