You guys realize it's rather frustratring as a portuguese to see Brazil and Kongo in the base game while Portugal ...
While I may understand case of Brazil (as it is colony of Portugal), why Kongo? It was not a country founded by Portugal or even dominated by it, it was its faraway partner and enemy for two centuries. It is perfectly feasible to see Kongo but not Portugal (regarding culture, because firaxis never cared about rankings of 'historical importance' which would be clearly in favour of Portuguese civ in this duel).
Also, you should realize that Portugal is, after all, Western European civ with culture close to Spain and Brazil, so putting all three at once is a little bit redundant and some ethnic/cultural variations would be preferred; and because Portugal is smallest nation of those three, it was chosen as the one not to appear on release

Meanwhile Persia is not only one of most important civs in history and over 2600 years of history, it is also very distinctive culturally (no, not at all similar but very different from Mesopotamia and Arabia - if anything Persia is culturally close to Caucasus and Central Asia), and that's why many people are disappointed by the lack of Persia: it is commonly viewed as one of 'main' 'baseline' civilisations. Portugal has high status in civ series but not as high as Persia, that's why many people would like to see Persia before Portugal.
Regarding historical importance, Portugal>Brazil, Kongo for obvious reasons, but Firaxis doesn't choose civs according to logic or importance but rather basing on uhhh 'we add whoever the hell we think is interesting and sells well'.
