That’s right but the real issue is enforcement. The council aren’t going to send compliance officers around to check who’s using your visitor car spaces. However, if they know their DA has been breached, there will be fun and games the next time anyone in this building – or the OC itself – puts in a DA.
Also there is a simple principle that by-laws can’t overturn superior laws (in this case, the laws under which the DA was originally provided). In fact, unless I’m reading this wrong, the decision to hive off the parking spaces is illegal on that basis and should be struck off immediately.