So did Hoshi manage to take over the Empire? What about the technology of the Defiant? Did it push the Empire forward or was it lost before it could make a difference?
The
Enterprise Mirror Universe episodes took place before the Mirror Universe episodes of the original
Star Trek. As far as I know, from what I read in the Mirror Universe story collection, the story
Age of the Empress, Hoshi did, indeed take over the Empire (picking up right where the last episode left off), had a coup against her by the Andorians (whom she personally invited), only to use the Rebels that had been formed by T'Pol after she managed to escape from capture to regain her throne and the story ending as Phlox works on resurrecting a dead Captain Archer through abnormal medical technology. Some may not consider the story as canon, however the story itself was based on a treatment that was meant to be another Mirror Universe episode for the show had it continued on. But I also heard there was another story that was written that takes place after the
Age of the Empress story that continues on after that (I can't say for certain if its true or not, nor can I say I've read that one). And Empress Sato, from what I've also read somewhere online, her version of the Empire after the story (in which due to T'Pol's actions in helping getting Sato back on the throne, allowed for the Vulcans and the Terran Empire to be equals instead of the Vulcans being repressed as it was in the episodes) lead up to the eventual turn around cause by Mirror Spock in the "Mirror, Mirror" episode 122 years later and its eventual fall.
As for the Defiant, I think all it did was give the Empire a bit of a push for advance technology at the start, but had ended up being as advanced as it could be much earlier than Starfleet had in the normal universe. So, I'm guessing that the Terran Empire had ships like the Defiant for years (which, lets face it, it would have taken some time to reverse engineer everything on board the ship, as well as finding the necessary materials and resources to construct them) and then, the Terran Empire and Starfleet eventually met at a point where both their technologies were the same (with the exception of torture devices, obviously), which accounts for why the Mirror Enterprise was only slightly different from the Enterprise of the regular universe.
That or somehow, the 29th Century and their time traveling ships of the Mirror Universe recognized that the Defiant was there when it shouldn't have been, gone back and destroyed it. I'm joking of course, honestly, I believe more in what I said above than this idea of the time traveling 29th Century people.