You know, I have to say I never got the "Nintendo's Lightning" label that people kept throwing around, at least not from who the term was used for.
From my understanding, the term basically means a character that was forced into promotion and prominence regardless of their previous popularity or notability in the franchise. The reason being because Lightning was (supposedly, I didn't follow FF too much at the time) heavily pushed from the get-go with FF13 and that continued into FF13 LR and was thus 'forced' into the spotlight unwarranted. However, looking at the characters people kept applying it to, it doesn't really work for most of them. For example, with Rosalina Nintendo didn't start pushing her until years after her debut. Hell, between the Galaxy games and 3D World, her only appearances were spinoffs like Mario Kart, so right from the start the comparison doesn't work as they gave her time to see how her popularity held rather then start right away. Additionally, the character was very popular when she debuted, I remember the positive reception she got with Galaxy and I similarly remember the disappointment when she was downplayed in the sequel. So it's not like the character started from nothing and Nintendo pushed her into prominence, she started with a great base in popularity and Nintendo continued off of that. So on both counts, you don't have a character that was 'forced' into the spotlight, you have a character that the company saw was very well-liked character and decided to make her a mainstay. That doesn't make her 'forced', that makes her a character who earned her way into being one of the most well known characters in her franchise. Same with characters like Lucario, Isabeau and the like, yeah they're new characters that are now in the spotlight with older ones, but the reason why they're there is because after seeing their popularity over time it was capitalized on, not because the company made them into that role.
So really, it does seem like the "Lightning" terminology is more geared towards throwing shade at newer characters becoming mainstays rather then an actual critique of how it happened. There's not a lot of reason to call Rosalina a "Lightning" unless you just don't care for the character and how she's used nowadays, as it's not like her popularity has come out of nowhere. There was a case to be made for her to grow and become a mainstay and that's what happened over time, it wasn't sudden or forced, it was gradual and took some gauging. So it's not exactly fair to call her a "Lightning" in that regard, she did earn her keep, and that rise does seem to be warranted.
