Aggressive factions are unrealistic

[Populus Romanus]

Arche Seleukeia and the Ptolemaic Kingdom are both examples of Super Powers as well (although their sphere of influence was confined to a smaller area of the globe). Furthermore Achaemenid Persia was also a Super Power of the East.

Your example of Lusotanna is ridiculous (other than that they do have a tendency to go on the rampage in EBI). The Lusotannan were a people who were pastoral with very little in the way of large centralised government (and by very little I mean none). They never developed the bureacratic complexity to administer conquered lands for any length of time, and had no need to do so - they were successful enough as they were. That would be like me saying that because the Pacific Islanders havent developed into a Super Power, we should dismiss the case of the United States and Soviet Russia.

Of course Super Powers are the exception not the rule in any given time, but thats because a world stage cannot accompany more than 2 or 3 by definition (if the world was replete with super powers, they wouldn't be super powers).

I don't think you've made your point at all, and the collapse of nations and tribes to one faction was common throughout all eras until only 2 or 3 are left standing. Its an arms race, the size of the powers dictated by what is politically and socially feasible at the time.

Foot

I would hardly say the Seleucids and Ptolemys are good examples, after all they never conquered any of their territory. It was all conquered for them by Alexander. Indeed, they are fragmentations of a larger empire. And they, for the most part, never expanded much. For the majority of their history their borders remained static, with the regular, but very small, fluctuations of the border either way. Mostly, however, their borders would shrink rather than grow, though this applies to the Seleucids more than the Ptolemys. The Seleucids in particular were held in check by rebellious satrapies, though I do not know what exactly was holding the Ptolemys back. Also, the elimination of nations until their are progressively fewer and fewer nations is not inevitable. If it was, why isn't the entire Earth one country? If the constant assimilation of power was inevitable, then that is what inevitably would occur. However, the entire world is officially divied up between 100 to 200 nations (I'd rather not look it up), although that is an extreme understatement given all the regions of the globe where "official" nations have no juristiction whatsoever.