The median DM accounts for half the talk time at the table, as much as all the players put together.
That’s measured across whole nights and the middle of the distribution is quite tidy. Half of all tables land between roughly 40% and 60% DM talk time. Whatever else varies from group to group, the share of the evening coming out of the DM’s chair mostly doesn’t.
It barely moves across the night, either. The DM’s talk share runs a touch higher in the first twenty minutes (the recap has to come from somewhere!) and drifts down as the hours go by, but the whole slide is about five points over four hours. The night starts as mostly the DM’s voice and stays that way, more or less, until the end.
One table in ten has a DM under 30% of the talk time. One in ten runs past about 70% (most of the night in the DM’s voice). A lot of the extremes is just table size. A DM running a single player speaks about 70% of the night. Add players and the DM’s share falls, but slowly. 53% with three players, 49% with four, 40% with seven. In fact, it seems that adding players takes a bite out of the other players’ talk time and only a small amount out of the DM’s.
One more thing about the extremes. Tables with a talkative DM spend about as much of the night in combat as tables with a quiet one. Where they differ is roleplay… about a third of the night with a talkative DM, about a quarter with a quiet one.
Overall, it seems like half of the session is what you get when one person plays the shopkeeper, the villain, the weather, and the rules.