I don't recall "taking over the Great Valley" as being part of their plan. I am pretty sure their plan was more on a global scale.
As for their diet, I'm still siding with the "fish eater" argument, as it seems unlikely that they are leaf eaters. Pterano and Petrie are supposed to be fish eaters as well and yet they have flat teeth. Also we do see flyers with sharp teeth in LBT5 and they are clear meat eaters. So why would they give sharp teeth to a meat eating pterosaur, but then also give sharp teeth to another meat eating pterosaur?
The pachys could be omnivores, which would explain the sharp teeth. I should also point out that some herbivores do in fact have some sharp teeth, so it's not really that unusual.