well, it does work...just
it actually works as well as VoIP extensions. If you have a number of VoIP extensions in a hunt group when you pick up the call on one device the others continue ringing for a bit until they are told the call has been answered. Now, depending on the device, this can be as little as a single ring but can often be a couple of rings later. This is down to communication from the exchange and response time from the devices. In the case of your iPhone, it is “the exchange” and the MacBook and iPads etc are the extensions in the hunt group. As the calls are pushed to the devices the call pickup also has to be pushed so they know to stop ringing, this is why it can take a few rings to stop.
this has been the case since apple introduced the feature. I have never had calls ringing out of sequence though, e.g. call starts to ring on iPad long after the call has been answered on iPhone. That would indicate a huge push notification delay.