I believe you are thinking of the Prometheus prototype. I don't recall this being mentioned in any of the movies with the Enterprise-E. A check of Memory Alpha supports this.
We don't know what other kinds of ships have this tech, if any, or if it can be retrofitted. Since it was mentioned as a feature of a new prototype, it is likely a very new thing, and not necessarily found on ships that were designed years and years before that prototype.
I agree with your post above. Most of the stuff on Sov is laughable, especially since it's only 5-10 years younger than Galaxy, to say that it's some uber advanced warship is pushing the limits of my ability to suspend disbelief.
As for regenerative shielding, I am willing to give it benefit of doubt, may be it was retrofitted for "nemesis", or may be it was there, since Geordi does mention that it is the most advanced ship in the fleet.
Either way, it doesn't necessarily mean that it's shields are far superior to that of Galaxy or Nebula, it means that they recharge quicker, but since Galaxy/Nebula are so massive, their raw shield power output has to be greater than Sovereign's. In Star Trek, bigger is always better.
Bigger ship, more power, more shield generators = stronger shields.