In grand strategy there is a concept of a "tall empire" and "wide empire":
Wide empire - a large number of adequately developed cities.
Tall empire - a handfull of exceptionally developed cities, whose economic/military potentional, can rival a wide empire.
In recent TW games you were pretty much stuck with "wide empire", because cities are hard capped in their development. A single province can't provide you both economic and military superiority. You always go for more and eventually end up with an empire of equally developed cities. Yes, there are some recruitment provinces and some unique upgrades, but overall the cities have pretty much the same level of development.
Now, the upcoming "Realm of the Wood elves" DLC features something, that is very similar to a "tall empire". Wood elves have just Athel Loren, but it has more room to grow, than any other province. Forest dwellers don't acquire new provinces, but erect outpost, which will fuel their economy and military in Athel Loren. That might be the first legit "tall empire" in TW game, because now you can actually win Campaign with just 1 province and even rival wide empires. The question is - to what extent? Is max capped Athel Loren on par with wide empires Empire/Vampires/Dwarves, who have occupied every possible territory?
Anyway, I am very happy to see that kind of empire building finally making it's way into TW series. Not only it will do a good job for Wood Elves, but also for Chaos Dwarves (if they ever make it into the game it is). They have pretty much similar approach to the state, where they hoard all the manpower and wealth inside - Mingol-Zharr-Naggrund, while the rest of the land is pretty much fortresses or slaver camps.