Sableye is one of the most dangerous donkers, but there are only a very few decks that can take use of this ability without ruining their consistancy. In DP-SF, the only viable decks that run four darkness energy are Tyranitar variants and some weird T2 decks around stuff like Honchkrow or Houndoom.
If the deck doesn't run special darkness, it only beats Gastly. Dusknoir players can use the shiny Duskull to prevent it, although this is somewhat expensive. And even basic Darkness is usually only teched and not very common at the starting hand.
Once you have a chance to play, there are lots of possibilities to fill your bench, so if you have 4 Call, 4 Bebe, 4 Rose, a Luxury Ball and 7+ other basic Pokémon, there are 20 cards that can help you - very unlikely you won't get one of those in your first 8 cards. So, once the first turn is over, it's no longer that dangerous, even if it has special darkness in the deck.