I think Dragoon should stay. It feels appropriate because I'm reminded of the Dragoon class from Final Fantasy that has the "Jump" ability.
"Marauder" would be good for the Chimera, as they're sort of a hit-and-run class.
"Basilisk" I think would be better for the Hydra, since Basilisks can traditionally turn people into stone, and Hydra's have that freeze ability.
Builder -> Granger
Soldier -> Dretch
Hydra -> Basilisk
Chimera -> Marauder
Dragoon -> Dragoon
Big Mofo -> Tyrant