It is. I don't think I ever played a game from start to finish.
I think the reason it took so long was it was so large scale. You had the ENTIRE GALAXY to conquer. I see the Space RTS as being more solar system based, where there's only a dozen or so planets. I guess it would be kind of like the settlement idea in AoM - you start with a town center already built on a settlement, then go out and capture more settlements. If you destroy enemy bases you can take their settlements over too. Exactly the same with Planets, except instead of giving you only a pop boost like in AoM you get a pop boost plus access to more resources. There could also be some resources in space that your construction crews (who build structures in space) can mine.