Sure, Fox has a shot at having a Lillard-like impact, just because he is so talented. But right now, he is closer to CJ McCollum in terms of value.
Dame takes and makes difficult threes, gets to the line and hits his FT, and makes plays for teammates. Everything Fox is good at, Dame still does better. The gap in terms of shooting is much bigger than the gap that exists in terms of Fox's physical advantages. Lillard isn't exactly Steve Nash running and jumping around. Even as a defender, Fox has not proven himself better yet, although I think he should be.