Let me start by saying, I'm not knowledgeable about Portuguese history but I just want to point out some logical inconsistencies.
First you say,
"There are a handful of kings that could have been chosen that would make total sense, yet no one can rationally look at the choice of Maria I as nothing more than "we need more female leaders, let's put her in the game". "
Then you say
"Your reply baffles me, for I do not dislike Maria I as Portugal leader in Civ5 because she's a woman. I dislike her being chosen because there were choices much more interesting and relevant. Just that. "
Those statements are not mutually contradictory. People keep confusing "I don't like that they only chose her because she's female" with "I don't like her because she's female".
It's perfectly possible to like the selection of (to use Civ V for examples) Elizabeth, Isabella, and Catherine the Great because they were important, powerful, and iconic rulers, while simultaneously thinking Maria I was a poor choice and suspecting that she was only chosen to fill some quota of female leaders.
Of course we can't prove that they deliberately picked Maria I over more important, iconic, etc. Portuguese leaders like Afonso I, João II, Manuel I, João IV, or the Marquis of Pombal simply because they wanted another female leader. Maybe someone on the dev team just had a strong interest in the Napoleonic era. Maybe they thought it was interesting to note that her reign began the first and only time in history a European country was ruled from a capital city in the Americas, and they didn't stop to think about whether the ruler who fled Portugal to hide in Brazil was really the best face to use as the game's representative of Portugal.
Or maybe they just wanted another female leader, browsed through a list of Portuguese monarchs, saw the name "Maria", and figured she'd do. Considering how ineffectual a ruler she was, and how bad a representative of Portugal she is, it would be perfectly reasonable to object to that without having any actual objection to her being female. If she had turned out to be a great leader on the level of Isabella or Elizabeth, what objection would there be to her inclusion?
I don't think most people would be happy if, out of all the monarchs and lords protector and prime ministers England has had, they selected King John as the face of England in the game. Maria I feels more like a Portuguese King John than a Portuguese Elizabeth. Her inclusion was a poor choice and a bad hand dealt to Portugal. And if it is actually true that they picked her because of some quota of female leaders, then her selection was kind of insulting to women as well. It's like they were saying, "There haven't been all that many actually good female rulers, but we want to represent you ladies, so we're willing to scrape the bottom of the barrel to find any women we can to make sure you don't get underrepresented!" I'm not a woman, and I don't consider myself competent to be offended on behalf of those who are, but come on now. If that's the best female ruler you can find for Portugal, then just bite the bullet and admit that Portugal is not the right civ to give a female ruler to.
As for Catherine de Medici, we already know that Ed Beach has a particular interest in her time period, and in her specifically. I don't think her selection was because she was female. I think it was because Beach is fascinated with her and thought it would be fun to have her in the "big personalities" incarnation of the Civ series. There are other leaders I'd have chosen before her, personally, but I don't have any particular objection to her.
(And to those people who say Joan of Arc would have been a better female option . . . how do you say "Ugh" in French? Joan of Arc is a perfectly fine choice for a Great Person, but not for the leader of the civ itself. In fact, when she was the female option for Civ II--the one that had a male and female option for every civ--as soon as I learned that it was possible to go into the system files and rewrite in-game text, the first thing I did was change the French female option from her to--wait for it--Catherine de Medici. She may not have ever been queen regnant--French succession laws were very clear that there would never be one of those--but at least she was an active agent in the actual running of the French state. That's more than Joan of Arc can say.)