It depends on the deck you're playing, of course - some decks actually want to play Karen as part of their strategy, like Eel Varients, so playing Karen over Oricorio in those decks is a no brainer. If you're playing a Fire Toolbox deck, you're probably packing several different EXs and GXs, so you probably don't have a great Night March or Vespi matchup as you're trading 2 prize attackers for 1 prize attackers (upping your counts of baby Volcs would definitely help this matchup, but that's for another post). I wouldn't run Karen in that particular case, because with Toolbox decks, you're trying to ditch unwanted attackers in your discard so you can keep your deck as thin and consistent as possible. The nice thing with Expanded too is you can more easily run tech Pokemon and just ditch them with Compressor when they're not needed. Which, incidentally, brings us to Oricorio's second biggest strength: being a one-energy attackers that can come down late and potentially win you games by sniping wounded Mons on the bench or piling a bunch of counters on a Shaymin (still played a lot in Expanded).