Dedicated Spellslinger probably can't be used to get rituals and preparations, as the free spells you get are based on your Spellcasting skill-- It wouldn't make sense to get a new Preparation to use with Alchemy or ritual for Ritual Spellcasting for improving your Spellcasting.
That said, Dedicated Spellslinger only blocks access to Summoning and Binding skills, not anything in the Enchanting group (or Banishing), so there's an argument to be made. I could bring it up with the errata team. Dedicated Conjurer, by the way, only blocks Spellcasting, not the whole Sorcery group, and again doesn't touch Enchanting. Unfortunately since these don't really do enough to justify the sacrifice, I doubt many Full Magicians will be getting them. Extra spirit types just isn't worth total loss of Sorcery, even with Alchemy still available, IMO.