Can get the angle between the camera forward vector and the vector between the camera and point with the dot product. This to me sounds like the same amount of complexity.

If you wanted to optimize you can go for a DistanceSquared check instead of a distance. Will save you an expensive sqrt call.

This helps understanding how you go from one to the other either in a positive or negative way without it it would be impossible to differentiate the inner from the outer angle formed between vectors.