Foxy Grandpa Builds?

Gunter and Frederick are pretty identical, so they kinda just do pretty much the same thing

Nope. Strictly worse than Frederick, and no unique skills. He and Jagen pretty much exist to pass on Horse buffs. Their status as veteran units gives them lower BST, but in Jagen's case at least there's not an exact better copy. I still use mine sometimes, but that's mainly cause there's so few green horses.