As you may know, after the Silmarillion was published, Christopher Tolkien revised the story, saying that Gil-galad being Fingon's son was an "editorial mistake" and claimed that he was Orodreth's. However, there are few pros in Gil-galad being the son of Fingon that make quite a bit of sense:
- His history is far more defined than it would be as the son of Orodreth. We would have more lore to grasp.
- No source ever mentioned that Finduilas had a brother, and what his role was in Nargothrond.
- His claim for the High King crown would be stronger. If he was the son of Orodreth, Galadriel's claim as a High Queen would probably be stronger instead by the order of succession. She would be older generation within the same House.
So I asked about this from Corey Olsen "the Tolkien Professor". His answer was that both answers were true in one point, and Tolkien never truly settled the matter, with Gil-galad being relatively late arrival in the legendarium.
So, cast your votes please.