To further my point.
Each Civilization in the game has 1, 2, 3 or even 4 available leaders. Each leader in the game has a pre-set trait value. The number of UU's available for each tribe in the game depends on the number of leaders it has available.
For example:
France: 4 leaders (Joan, Louis, Napoleon, DeGaulle). 4 Uniqe Units available, to the nation, not just one leader, for example: Trebuchet (it's a distinctly FRENCH unit!), Musketeer, Cuirassier, Foreign Legion. Because number of available unique buildings is generally a bit shorter, a nation with the max, 4 leaders, has at least 2 Unique Buildings and 2 added bonuses to existing buildings, or perhaps 3 UB'S and 1 generic Building with an added bonus(for a French leader only).
Then comes the matter of UA's. This would solely depend on the pre-made personality of each leader. For example: Joan of Arc, a Honorable, Spiritual and Militaristic leader, might get a UA boosting the strength/population happiness from religious buildings, while Napoleon's UA would certainly deal with a militaristic bonus of sorts, LouisXVI bonus would be a cultural one, and DeGaule's a mix of military/cultural UA could apply.
Now, for nations where it's difficult to come up with more than one leader, or not so much leader, as more than 1 UU and UB, well, WHO IS ORDERING ALL NATIONS TO BE ON EQUAL TERMS? ZULUS, for example, might still have only 1 great leader (Shaka), UB and UA, but still, when he's in your game you still might be in tough with his Impi, especially if he gets lucky and is dealt excellent land for expansion at the beginning of the game.
Face it, some nations shaped the history of Earth's Civilzation, while such as the Zulus, or Polynesians, while significant and unique, could not compare to the likes of Rome, Greece, Great Britain or China in the scale of Cultural, Military, and all other forms of Civilized Discovery and Domination. And if you deny this, YOU ARE FOOLING YOURSELF!
In CIV V, when I see. for example the Shoshone, Huns or Zulus culturally leading Rome and/or Greece, it makes me laugh, everytime.