You are considering that datadir is a sibling to the symlink's directory. I, OTOH, consider that datadir will be most probably a sibling to the original script file's directory (because you can symlink it from anywhere, and considering otherwise would be a security risk *). We will have to agree on disagreeing.
* create symlink, create malicious configuration file side-by-side with symlink, ... profit!
Update: I stand corrected about the (meaning of) final destination of the datadir according to the answer by AZed below... You're welcome! And seems that we will have to agree in agreeing :-)