Yes I (and many others) will need dongles. In my case, I do photo and video editing with some equipment that has ports / connections that are not removable. New cables will work for some cases, but not all.
In Every "pro grade" powerbook / MacBook Pro ( that I can think of, and note I am omitting "MacBook") ever since the G3 models, there has been a stepping stone, mixing old ports with new. Last I checked, the new MBP is still far thicker than a standard HDMI port, SD slot, or , legacy USB port.
Mine is rarely home, and is running off battery 80% of the time, so I don't fit your complaint case. That said, I don't really feel I need to work out to carry my laptop. My camera gear, lighting, tripods, and other items could stand to lose some weight, but I don't have any expectations of that. My current retina MBP is lighter than my older non retina MBP, yet, I don't even notice it when carrying 2 cameras 4 lenses, and 3 flashes in one bag.