Moenbryda was objectively a more developed character by the time they killed her; Established background, romantic interest, driving purpose. Minfilia is bland and boring despite having been around for literal years of development prior.
Hell, even Thancred's story played out over almost the entirety of the MSQ, and Alphinaud's failure serves as the crux of his development over 3.0.
Hell, even Thancred's story played out over almost the entirety of the MSQ, and Alphinaud's failure serves as the crux of his development over 3.0.