[DJM83]

Depends, ive never built a BMC, but most of not all bikes ive built. The brake hoses/cables are already installed. Some cheaper bikes you have to install brake callipers and sometimes even attach a cable to the rear mech. Dropper post cables are really the only thing, and even then the outer cable housing is already in the frame.
Electronic shift bikes are super easy to set up shifting wise.
Its moreso having to replace hoses/cables when they are stuffed.
Id imagine possibly your BMC at that higher end has channels inside the carbon frame so slide hose into the frame and its guided to the exit hole at the back. Also road bikes dont have the pivot point like mountain bikes so the hose/cable only goes in the frame once then out.