Has this particular scene always been perceived as unintentionally hilarious?
Somewhat? It's ridiculously melodramatic, and it happens so early in the series that I suspect it might turn people off to what was a really good show.
So, who's Ina's presumed-dead older brother, who is masquerading as the dictatorial world government's private military contractor's top ace pilot?
Hard to say, since Ina is kinda their ace to begin with. I'm gonna say Calli, with Kiara being a very keet take on Noin. Gura would have to be Wufei, since she's the apex predator.