Another reason that the sabertooth salmon dossier was released first could be that they need more easy ressources of fish meat when they introduce the new aquatic life cycle. Or they put more effort into the other dossiers and work out something more difficutl to give them a new special use and make them look cool just like they did with the titanosaurus. Because more people wanted a Basilo for example, they probably just put more time into development so the majority is satisfied.
Edit: Probably they will work out another use for the sabertooth salmon. Since the Coel will be available in different sizes, the same thing could happen to the sabertooth salmon so that the big ones could reach about 9 feet and are tameable and ridable then.