First, the possibility of evil or simply anti-Sylvan wilderness characters were something we thought about in designing and balancing these powers. I don't know if it will make you feel any better, but this isn't something we simply overlooked. There are angles (potentially in your favor) that you might not be seeing yet.

Second, a skilled (or even competent and willing to team up with Sylvan's enemies) enemy ranger is probably one of any Sylvan's worst nightmares, and if it's not, it should be. Let them fuel your character's hatred and work your way up. Payback, they say, is a bitch.