Parmandur
Book-Friend, he/him
Just anecdotal. But I don't see many mentions of ongoing campaigns set in Ravnica in online chatter. Mystara campaigns seem to get mentioned more often.
Are you playing in a Ravnica campaign?
I am not, but I am paying attention to what people are talking about, and buying on the DMsGuild. Anecdotes are not explanatory, though I am sure WotC has some hard data on usage of the book as they ahve access to a slightly larger sample size of the millions of people playing than either of us.
We have Tieflings, Aasimar and Genasi already.
But not Rogue Modrons, Bariaur, or the "Plane-Touched" race they have mentioned (classical 2E Tieflings)
The DMG does just fine as a broad overview. You either need detailed content of a small location (Avernus, Sigil) or a few paragraphs with special rules, as in the DMG.
Could just as easily go in an adventure.
Expanded gazeeter material is always popular.
You mean like Ghosts of Saltmarsh does for nautical adventures...
More like the 50 pages in Guildmaster's Guide to Ravnica or 100 pages in Rising from the Last War: expansions ot Chapter 5 of the DMG, for the specific genre of the setting.
MToF is already the planer monster manual.
A monster manual with some planar elements: there are oodles of 2E era Planescape Monsters, and others, to draw upon still.