Ctis is hardly underpowered. That said, they do need alligators in their swamps for thematic reasons!
http://urbanlegends.about.com/library/bl_gator_deer.htm
This is NOT a huge gator though. Only 12 foot or so. In the 1800's in Louisiana Gators reached 20 feet in length. In the times of MA Ctis, who can say how large the Gators may have grown?
Of course huge is a relative term. If you were in the water and it was staring at you, I am sure it would look enormous.