Either way works. Really depends on the DM and what their desires are for the games they wish to run. If a DM is open to all kinds of possible games, then yeah, the group of players all working together to come up with a theme for the campaign will work great. But if the DM changes themes with each subsequent campaign they run so as to make sure they are each different every time, then they are good to makes the decisions in my opinion. And if the players don't like a particular theme then they can choose not to play in that particular game and wait for the next one.Eh.
I think a better framing than having a "DM establishing setting expectations" is . . . having a session zero where campaign style and theme is discussed. If the play group decides on the circus troupe, great! If the play group decides on a mostly human-centered campaign, great! If they all want to play dragonborn (like my middle school students), great! And, of course, the DM is part of the play group! And if they're doing a lot of prep work, their vote should probably carry a bit more weight, but also shouldn't ignore what the other players want out of the game.