@Josh103
DLC is definitely not essential for Cities: Skylines. I only have the one for new transport stuff and even that is only because I want to have monorails in my cities, not because I thought I really needed it. And I
really want to have the latest one, that adds park mechanics and probably will get it when I pick up the game again, but it’s still not essential.
Now, admittedly, those DLC did add some things that one could deem essential and they really improve the game. But: You don’t have the buy the DLC themselves for them. Instead, they’re added in a free update that comes out at the same time as the DLC itself. For example, aforementioned transport DLC added new features for traffic control, which you got even if you didn’t buy the DLC (which really didn’t add much more than new kinds of public transport).
On other cases, they added cosmetic features in free updates, that only get gameplay-relevant when you have the respective DLC (as happened with the day/night cycle).
Cities: Skylines’ approach to DLC is pretty great.