so one thing that I've noticed is that there's just not a lot of bad guy stats out there. The core rulebook has NO animal stats at all. I find myself having to reskin baddies or use online content to determine species stats and i was wondering why these rpgs haven's just come out with a baddies compendium that just has a whole bunch of useful butt kicking and butts to be kicked bad guys.

Have you checked Edge of the Empire Core rule book? There are stats for all manner of beasties in there including Rancors.

Check out the link in my signature, I've got custom stats for a leviathan and Rakghouls available to download.

Seeing as Age of Rebellion has a focus on the Galactic Civil War, I image they don't put many creatures in the books because generally you'll be fighting Imperials. Edge of the Empire and Force and Destiny have more animals in them, along with the supplements. Suns of Fortune and Lords of Nal Hutta has a host of many different ones, and all the adventure modules (excepting maybe The Jewel of Yavin) usually have a variety. Strongholds of Resistance has several, but nothing iconic, while Stay on Target has a variety of mounts (bantha, dewback, varactyl, among others), of course.