There are a few trends in people who want to build a strong team for their playthrough, but also want to play the game "as intended" (e.g. no competitive gimmicks, only Pokémon that can be reasonably caught over the course of a typical playthrough).
Wide type coverage is a given, but it's especially noteworthy that you'll usually see at least three of the big four elemental types (i.e. Fire, Water, Grass, Electric). The exact composition of them depends on the chosen starter, since starters are usually the best option for that particular type.
In Brilliant Diamond and Shining Pearl, the consensus on the best option for each type appears to be:
>Fire: Infernape/Rapidash
>Water: Empoleon/Gyarados
>Grass: Torterra/Roserade
>Electric: Luxray
Given that Fubuki already has a Monferno and Luxio, there is no doubt in my mind that her original goal was to create a sort of quintessential strong regional team, but with only shinies. This Magikarp was definitely going to be a Gyarados at some point. It's really just a question of whether the amount of time she's spent on it has caused her plan to change.
