Note that it's not automatically six but I understand what you're saying.
It does depend a lot what kind of "desert" starts they end up with. If they start on the edge with only 1 desert tile next to the city centre, then that might be a tough start for them. I think the ideal to me would be having maybe 3 or 4 desert tiles next to the cap, so that you still have 2-3 non-desert tiles to work early on.
They're also going to run into amenity issues early on if they do grow too fast. Probably not a problem if they have useful tiles to stretch to, but they're going to need to manage things to make sure they don't expand too fast into useless desert tiles.