Paradox doesn't seem to have much issue with it for multiplayer. Is the Civ multiplayer base really that naturally disparate?
As far as I'm aware, with paradox games (i.e. Eu4 with has twenty million small dlc), you use whatever DLC the host has (even if you don't have it).
For Civ, all players need to have the same DLC.
This might be a technical decision (i.e. eu4 being more lightweight*, the host's computer can do most of the calculating, while for civ each individual computer does the calculating) or a business decision.
edit: *Just to make clear that I mean lightweight in terms of computer power needs, not trying to start a flamewar over comparative strategic depth