Humans on Earth have adapted to living in the most extreme environments and that is without magic that can literally stop earthquakes or create spontaneous shields that block weather. Nomadic peoples are still people with culture and society. People cut farms into mountainsides, planted them in deserts, cultivated and shaped the Amazon. Again, many fantasy settings and real civilizations are just this: scattered rural villages, a few big cities, vast wilderness. The Roil sucks but the Zendikari are not living on Grixis or New Phyrexia, which count more as hellholes imo.
I'm repeating myself, but I really like this conflict set up between Nahiri and Nissa as white intervening to build up large structured, stable societies versus green letting people live and adapt within nature.
Odyssey-era Otaria (two big cities, scattered villages, and a bunch of nomads)
Not that I care about Zendikar or anything, but for what it's worth, Odyssey-era Otaria technically also had the (pretty sophisticated) city of Eroshia, the Mer Empire, all of Tamingazin (at least retroactively) and several fiefdoms and smaller kingdoms that weren't really relevant to the story (we know that from scenes in the novels that are set in Topos and Eroshia).
Thanks for the clarification.