I assume you're refering to TA. There, the Yor are heavily underestimated. They are difficult to play, with all their one-per-planet buildings, some important yellow-techs missing, and in fact, expensive planetary improvements. In TA 101 they've been labelled pretty weak because of that; and the AI can't master them; esp. because they've been nerfed to 50% natural abilities (which can be changed, though).
Point is, for everything there's a possible workaround and if the way you setup this game does allow this, then the Yor are invincible.
One workaround for their expensive planetary improvement is either choosing Breeder or Hive for SA. In the first case buying all improvements. Their starting techs/improvements outclass every other civ in TA by far, so you can have a very strong game right from the start. This will lead to strong colonial rush, and lots of planets are a necessity to mititgate the one-per-planet limitation of the Research Matrix.
The economy really isn't that big problem. First, their improvements are pretty powerful, but take as good as no maint. So you actually don't need that much money; but their 'Efficiency Studies' are better to research than the "Star Federation" branch, so first bonus. Second is, their econ-techs are untradeable, while the Yor can actually trade for Yellow-techs or Banks from other civs. So, if that time is near, the Yor will clearly have a much better economy than everybody else (and they can mine out Econ-resources pretty well, too);so subsequently they could upgrade the #1 tier factories to the end-tier one, which beats everything else in production.
The only thing that bothers me is that their Miniaturization-bonus has been nerfed (again).
