Per the manual, all Phantom 4 models and the Inspire 2 can be connected with only a micro USB cable.
All DJI supports reps are not equally knowledgeable. Some know more than others. Some offer incorrect information. In most cases, it's better to trust the manual if the information you're seeking is contained within.
The manual actually says on page 11 that the Phantom 4 Pro and Adv need HDMI
Got to agree with you about their support staff, some of them are clearing reading from scripts whilst a few have some knowledge.