The historical galaxy is actually fairly balanced. al-Malik have the most resources by a long shot available to them (because of the Symbiot planets, which are easy to conquer in the late game). Decados have a pretty good selection, especially with a barren world and a desert world. Ultimately energy, trace and gems are how your empire's strength is measured. Li-Halan are similar to Decados in the resources. Hawkwood have the fewest resources. But they also have planets next to Byzantium II and the most gems early on. And Hazat have probably the fewest planets to naturally expand to, but practically surround Byzantium II. So I wouldn't say any house has a real tangible disadvantage to anyone else except maybe Hawkwood.
The AI is really why this game didn't get higher reviews than it did (usually 60-75%). It simply loses its luster when you find out the AI cannot defeat you. Even if you are awful. They will never declare themselves emperor. So the only way for you to lose is to lose all your nobles. But they won't land troops and attack your home planet. So even when they patched them to build more units, more cities, and so forth, you still could not lose unless you intentionally went out of your way to lose your nobles. Human games make it so much better.
The graphs are fairly accurate, but ignore the score. The score takes a lot of things into consideration, including money, research, units, value of units, if you've signed the holy writ, etc. Your score can go down on the same turn simply by spending resources. The unit/city charts are accurate in raw numbers, but it doesn't necessarily mean power. 20 Cadiz Dreadnoughts won't show up as many units, while the AI loves to spam low level, weaker units even at the end of the game. Also, the AI is completely impotent in the Nova patch because of the immobile emplaced guns.
And as for the Symbiots, they're another unfortunate bug. They are formidable units, and can expand very well. The caveat? They do not build spaceships, and you really have to change the whole exe to change that (I think Hyperion managed it). And the new units they build are 0 loyalty, making them very easy to route. If those two bugs hadn't existed, they would have remained a threat for entire games, adding an entirely new dynamic. As it is now, they are only a threat so long as they control space transports.