During the livestream rebroadcast of “07 The Throne Room,” there was some debate in the chat about Queen Ullara’s use of Dimension Door on Grog (3:40:26). Specifically, Dimension Door states: “You can also bring one willing creature of your size or smaller who is carrying gear up to its carrying capacity.” (PHB 233) Since Grog is huge and duergar are short, clearly Matt took liberties?
Here’s where we play rule lawyer: Duergar and Goliaths, despite their height and weight differences from Humans, are both Medium Sized. By this definition, a gnome could also still transport a slightly-taller halfling.
If we were to go by the stringent “goliath is bigger than a dwarf” logic, at what point do we draw the line for what qualifies as bigger? Technically, Lady Briarwood would be smaller than Lord, yet it still makes sense for them to go together. For simplicity, it’s just easier to use the general Size description for the use of the spell; your DM’s mileage may vary (and the street goes both ways!).