See this is where they get you ... Technically the basegame runs and works as intended. But, it's also boring and doesn't contain what is essentially part of everyday life for most people in a life simulation game.
- Need some different weather in your world? That'll be $20-$40 more
- Does your Sim want a higher paying job? You need to go to university for that. That'll be another $20-$40
- Oh you'd like to have animal companions complete your family? Just give us another $20-$40 and it's all yours.
Those 3 items right there, that should be included in a basegame (but never has been) and would make the basegame feel more "complete". Those are basic items that most people encounter every day. A life simulation game should also include those things in their basic basegame.
They don't need to be super in-depth for the basegame, just something basic that represents life:
Basic rain, snow, cloudy, or sunny days should be included in the base game. More severe weather (blizzards, thunderstorms, hail, etc) and weather activities, such as raking leaves, playing in puddles, shoveling snow, snowball fights, etc could be expanded later on in DLC.
Cats and Dogs are typical pets people have and should be included in the basegame. They could be expanded to include smaller animals and more pet activities, skills, and pet objects for them in later DLC.
Basic higher education should be included in the basegame. It doesn't need to be this in-depth system where you follow your sim to university and live there, join in clubs, have protests, have keg parties, etc, but even just a rabbit hole type of school, where you get pop-up notifications of how your sim is doing. Then they could expand it with more degree types and all of the normal DLC stuff that people crave to
have.
So yeah, in my opinion DLC is necessary if you want to represent "life".