I think part of it is that you can use a break that is ideal for the ghost but not for competition. When I’m struggling with the normal side rail break, I’ll put the cue ball in the centre of the table and just focus on getting an even spread across the table. And if we are talking about the magic rack and using the same tables, players can probably get dialled in but be an underdog in a new room on different tables.If they are that consistent, I don't see why their fargo ratings would stay so low. If they're good enough to "slap the 9b ghost around on a 9' Diamond" then why are they not winning more? Are they that bad at the other parts of the game?
EDIT: But just anecdotally it seems like skills sets vary quite a bit within similar ratings because I’ve heard from some players at the 630-650 level that they torture the ghost, but then others say they really struggle. Certainly there can be some exaggeration, but I do think that a lot of ghost practice may end up making you very good at the ghost and have diminishing returns in match play, unless you make sufficient adjustments.