If we're going off of Cynthia's champion team in Plat, and Lusamine's SM team, then Lus would definitely win. If levels are disregarded, as they should be in this case, as if they weren't, then characters like Alder would be stronger than Cynthia because his team averages at level 75, while hers averages at 62 despite them both being champions and narratively having similar strength due them both being champions. Since Lusamine only has 5 pokemon, it should be fair to give her nihilego so she can have six. In the SM cutscene, they actually show her releasing it from a beast ball so she can merge with it, meaning that she owns nihilego, and her using it in battles does not require a stretch of the mind. Disregarding Lusamine's totem skills(of dubious legality), her Clefable counters Spiritomb and Garchomp. In addition, Cynthia doesn't even have a single steel type move, despite having a Lucario(which, keep in mind, is also part fighting, meaning that Clefable can still hit it neutrally and doesn't have to worry about steel moves, as said earlier). Cynthia has two poison moves to counter fairy, one coming from Roserade and the other coming from Gastrodon. Gastrodon can't STAB the poison and Roserade is checked by Clefable's Psychic. The reason why all this Clefable stuff is so important is because Clefable has cosmic power, magic guard, and moonlight, making it a bulky monster. Also, Lilligant checks Gastrodon and Milotic with 4x and 2x effective moves, respectively, Misdreavus has Mystical fire for Lucario and Roserade, and Bewear can mess up Lucario as well. It's possible that Lusamine could win with just Clefable, Nihilego, and Lilligant, so a win against a full team with another full team is totally possible for her. Still hate Lusamine, though.
