so what are we calling the mirror feds these days?

The Terran Empire or Terran Federation ?

Terran Empire, hasn't that always been the name?

according to Smiley no... its the terran federation
according to shelly yes its the empire :S

haha darn Smiley

I think officially it is the Terran Empire. It is more commonly referred to as that instead of the Terran Federation.

Anyone else find it strange that the Terran Empire that we saw in the 2370's, which was portrayed as a ragtag rebellion, fighting a resistance war against the Alliance, suddenly 30 years later is creating the latest and greatest Starfleet ships, and seems to have amassed a fleet equal in size, or larger than the whole of Starfleet?

Not really, looks more like cryptic decided to simply ignore the ds9 mirror events.
Which frankly should be ignored given that the writers had no clue what the mirror side is about and messed it up.

Yes.

I put on the list with the masses of Trueway ships, which represent merely a splinter faction of the Cardassians from a race that was beaten to the ground in a war 30 years ago.

My theory is that they're from a different universe to the mirror universe in the show.

To explain it in more detail, lets call the normal universe 'A' and the mirror universe from the show 'B'. The Terran Federation/Empire in the game is from universe 'C' in which the Terran Empire never fell to the Klingons and Cardassians, which is why they have advanced ships like in our universe.
Furthermore, when the people from universe C complain about our guys crossing into their universe, they're actually mistaking us for another universe, which is universe 'D', which we know nothing about except they have been to universe C. In the C's attempt to attack universe D, they've accidentally attacked us (universe A) instead, basically its a whole big misunderstanding.
Meanwhile, The original mirror universe (universe B) is still out there, waiting for our captains in the game to finally encounter it and see it more like what it was in DS9.

I know thats complicated, but its the only way it makes sense in my mind.

I am now crosseyed.......and I still have no idea...you lost me at explain.....

Hmm...well, there's another thought. Remember how long it took them to build the Defiant in the Mirror 'Verse.

Who's the say that members of the rebellion weren't going into other points in Starfleet and taking ship designs to build more ships like the Defiant.

A couple years later, the rebellion manages to take enough worlds to start building more ship and with freed slaves, crewing them and taking out the Alliance.

I mean...40 years is a long time.