The whole "gates" thing seems like one of the riskiest jumps to me, actually. G'raha said the line in a side story arc in 2.5, which was January 2015. The 4.4 voice is September 2018. Even if you take the "we write the story two years in advance" thing to mean "we know every detail town to the thematic turns of phrase" (unlikely), that probably wasn't planned. Then there's that the 4.4 voice is explicitly quoting Loffrey of Final Fantasy Tactics (albeit more verbatim in JP).



To connect a G'raha sidequest line to a main scenario Loffrey reference because they both said "gates" is ... shaky.

Though look how many things in Stormblood were obviously not planned but look downright prophetic in retrospect. Thordan's darkened view of the Warrior of Light, Sephirot's lyrics, etc. Maybe it'll be another coincidence for the ages.