[jccooper]

Dragon is "berthed" to the ISS, unlike Soyuz which is "docked".

Berthing is what they do to ISS modules. It's basically bolted on--which requires a fair bit of work from the crew on the station side, both mechanically and in getting the spacecraft in place (which they do by robotic arm capture). They do this for the cargo stuff because the berthing mechanism is wider, lighter, and cheaper.

Docking is what you do for a manned spacecraft. They have fancy mechanisms to attach and detach quickly and mostly-automatically. It's complex and the opening is enough to get people through, but it's fast and easy. A docked spacecraft can leave on its own; a berthed one would require crew still on to help.

While cargo Dragon could take a person down to Earth, and they'd probably survive (probably nestled among bags of trash), it's not going to do so in a hurry, and since you have a seat on a Soyuz already, and it's designed for it, you might as well use that. Especially if you're in a hurry. I think the only time cargo Dragon would be involved would be something catastrophic happening to one of the Soyuz--but not to anything else.