I considered that too, but then who convinced them that they killed their dragon parents? Unless it was a massive and elaborate illusion type magic or maybe just a "edolas" style dragon thats mechanical but acts like the real thing. Either way they were "trained" by something and then got lacrima put in them and then killed the something that trained them, very confusing!

Maybe they will take over Sabertooth once Minerva is put out of her misery. But I do love the idea of a DS heavy guild :-$ or even some God Slayers too