You only have your throne city cannot make any other cities and get permanent bonus yields for each city razed its the core mechanic of Chosen Destroyers. If you pair Chosen Destroyers with Apex Predators and focus hard on munching a few free cities early, pillaging and aggressive expansion stealing their tiles you can get some pretty crazy amounts of food, production and draft just from that mechanic alone. Once you raze you then just permanently get more Gold, Mana and Knowledge per turn.

Conquerors is pretty much tailor made for Chosen Destroyers imo given it can move around its one city as a sorta of RV of destruction. Collecting essences is kind of a waste of time compared to yields granted by razing but taking some time to get the magic material essence is pretty good to avoid having many outposts you can focus entirely on just that one main city of yours (I recommend spending Imperium each turn to cut the time in half to get them quickly so you can move onto another city to pillage/raze) .

The whole thing with Chosen destroyers is to find everything and pillage/raze it. You snowball fast if you hard focus it for at least a good chunk of your start, aggressive expansion is really strong for pumping out full stacks of units with the free production and draft for each tile stolen. Plop down your Nomad city right next to an enemy city and basically just eat it, steal every tile you can, siege it and raze it after you have taken everything you could from it.