The key problems with 15 is 95% because of how it handles narrative (the other 5% is how it handles sidequests). Its because of that narrative structure and lack of focus that a lot of character fall into (though some are arguable) lazy or ill-matched tropes. Luna is very obviously supposed to be a clone-mix of Yuna and Aerith(more so Aerith)
Many characters have slight hints of interesting dynamics (both male and female):
- Cindy's upbringing is brought up a couple of times and is suggested to have been a key part in making her a workoholic. This isn't developed upon other than a reference or 2.
- Cor is seen having a guilt complex for not having been near the king upon his death. This is given only a single dialogue and is never expanded
- Regis knows MUCH more than he ever is shown to. He also only appears like twice in the game, so its never expanded upon.
- Don't even get me started on how pathetically non-expanded the "road trip" Regis and co. went on. Seriously wtf was that road trip about and why was it so important?!
- and with Luna, there are very very strong suggestions that she knew Noctis had to die and that both of them pretty much exist as just roles for the world. again, this is never expanded upon.
The game presents 2 main foils:
Ardyn and Noctis
and
Luna and Noctis
With Ardyn and Noctis, its very much a standard villain-hero thing that has time to develop between them. We see real growth and understanding through their foil.
With Luna and Noctis, its much more akin to Zero and X in Megaman x, but in relation the the idea of accepting a horrible fate. If you compare how Noctis acts before and after the time skip, he basically becomes Luna-like afterwards. He becomes accepting, moving and somewhat manipulative in events to try and facilitate understanding and prosperity while accepting self sacrifice. This became much more clear to me upon my second playthrough and looking at various cutscenes online again.
What I think they were trying to go for with the story between Noct and Luna was that they had different ideas relating on their fates, but both really just wanted to see each other again and be happy, and in a twist, they are never really allowed to until they both die.
The problem with Luna is that she isn't fleshed out nearly enough before her death, and none of the interesting parts of her character are really ever explored. Its because of this, i feel, that she ends up becoming a "woman as narrative push device" and "woman for the sake of the man" type character. I do not believe her character was ever meant that way, however. Narratives do a LOT in our perception of a character and how they act. Our LACK of narrative w/ Luna is a big big part of her problematic nature. I honestly think there were a lot of good ideas around her character and I do honestly believe that they thought they were making "a strong woman character", but missed the ball because they put what should have been a 50+ hour rpg in a 20 hour body.
I honestly think that if we had seen more of her childhood (maybe her mother explaining her fate about how both the Oracle and the King must die or something dark

) or maybe seen more of what she has done for the world (more scenes like the "healing the sick" cutscene) then we wouldn't be complaining nearly as much.