Curious question: Did you enable ascension victory, and if yes, how was a (relatively) quick ascension victory prevented?
No, I did not enable ascension victory. Avoided too early ascension that way.
Avoided too early tech victory as well. Wouldn't have really been an issue anyways, however, as I had the best research goin' according to the charts, and won before anyone could have gotten to an ascension victory anyhow. Disabling tech trading probably helped w/that, everyone moved up the ladder more slowly as a result, you only got what you researched. Tech speed was set to 'very slow', also. Disabled tech stealing even. Furthermore, I just played in normal, probably made it easier. (next game I'll bump it up to intelligent, but that was my first and considered it a learning experience). Having habitable planets only be occasional helped too, you have basically a shorter expansion period, but w/the immense map tech speed of 'very slow' still, so events get kickin' into gear sooner between the races, before too much of the tech tree has already been uncovered.
these were my settings, I'll probably use the same in the next game, but at the intelligent difficulty level:

Both parties need to have the Alliances tech (so trade it to them if they don't have it yet), and your relation have to be "close" or better. I agree that more in-game information about this issue would be nice.
Ah, w/out tech trading they just must never have gotten the tech. I probably won't waste time researching alliances then unless I know my intended alliance partner already has it. Good to know, will save me time. =>
Usually not a huge problem, because the Dark Yor are a minor race, meaning they don't expand. I actually never noticed that they have the same icon and color as the Yor, although both usually appear in my games. Still it would be nice if they had their own logo and color.