IMO, in Civ 6, going wide is the only way to really win. There are some penalties but they are minimal. In Civ 5 it was totally possible to win with one city, in Civ 6 that's almost impossible. So, if you like building large empires, I highly recommend it to you.
Yeah, that has certainly been my experience so far. In Civ 5 I'd generally take the culture/diplomacy route; I was able to beat one city challenge on immortal with a little bit of luck. In Civ 5, it just doesn't seem possible.
Part of the issue I'm finding is that real estate ends up being a real problem for buildings and wonders. You can't just indiscriminately rush and stack wonders - you'll simply run out of tiles. So, you're trying to place your cities in such a way to avoid land grabs by other civs, but not so much that they crowd out tiles for your other cities.
The barbarian spawning seems to be very unforgiving in Civ 6 as well.
