Sucks that Dark Sylveon is psychic type but I'm guessing that's because it's tournament legal
I'd wager that it's because those cards were designed with the format in mind. Honestly, you get a cards like Imakuni?'s Doduo that are never legal for tournament play, and exist only for aesthetic purposes, even if they would see no use and wouldn't affect the metagame.I think there's a good chance none of the promos are going to be tournament legal. The only reason I say that is because "Prime" isn't really a mechanic per sé. Because of that, there isn't a real reason why Dragapult would be banned from tournament play outside of "just because." Play-wise, there is no functional difference between a Dragapult Prime and any other Dragapult.
Granted, since Dark Sylveon V and Lance's Charizard V are V's... maybe that will allow them to skirt by? Odd since "Dark" and "Trainer's" pokémon ARE old mechanics not present in the current run of the TCG... Would they ban Light Toxtricity but keep Dark Sylveon V? It's weird.