I think the Channeler who weakened himself to create that extra city will no longer be strong enough to protect it from the Channeler that kept all his power to himself and then just takes over the area others have created.
Him and what army? Literally.
My Channeler will need an army?
From what I have read so far a Channeler has to expend Essence 'cleaning' land to build cities on or empowering heroes, casting powerful spells, creating magic items, etc.
You spend some of your essence on land to build a second city.
I spend the same amount on a Hero (Bob).
You spend some of the gold, mana, and resources you have on building up your new city.
I spend the same amount of the above on equipment and followers for Bob.
How is your new city going to defend itself from my Channeler and his band of adventurers?
In the long run the production of your cities will be a telling factor but the first person to attempt a second city is placing themselves in a weak position, they have to weaken themselves and invest a lot of time and resources before they get a payout. This happens in most games but everything I have been reading leads me to believe it will be more extreme in Elemental (I have to spend Essence as well).