My unpopular opinion is that DLC is not, in and of itself, bad. If you don’t want it, don’t buy it! If you do want it - great, no problem! In a world without DLC, you either have to buy the whole game, or not. If you tried it and didn’t like it, you have wasted the whole price of the game. Whereas in a DLC system, you’ve spent the price of the base game, but that’s effectively just a fraction of the total game price. You risked less.
What is a problem - and what I think most people who think they’re mad about DLC are actually mad about - is charging a price that isn’t commensurate with the amount of content you get. If a full game is “worth” $60, and it’s split up into a $20 base game and 4 $10 DLCs - great, everyone is (or, should be!) happy. But if the publisher charges $60 for $20-worth of base game and then charges for DLC on top, you should be pissed - but you should still be pissed about that mispricing even if the DLC didn’t exist. Yes, DLC is the reason why that pricing strategy is adopted - but that doesn’t mean that DLC itself is inherently bad. There are possible implementations that are not flawed.
DLC isn’t modular like that, you aren’t buying a fraction of the product and then completing the full thing with DLC. You’re still buying the base full priced game, and then DLC is typically additional content expanded upon that.
Your generalization doesn’t hold. Take Cities: Skylines (a city building game; compare it to Sim City) as an example. The base game cost €30 at launch [1]. It’s a (kinda [2]) functional base game, however, it’s somewhat flat.
If you’re interested in more challenge building industries (instead of just zoning industrial zones and that’s it), you buy the industries DLC (currently €15) where you need to juggle supply chains. If you’re bored by just plopping down some parks to make people happy, you buy the Parklife DLC (also €15), which allows you to be more creative in providing recreation opportunities. If you’re an old Transport Tycoon player and want to create the perfect public transport network, buy the Mass Transit DLC (€13).
The base game is fully functional without all these DLCs, and each one focuses on an aspect of the game into which some players might want to dig deeper, but not others.
[1] According to https://steampricehistory.com/app/255710 [2] I say “kinda” because it does have flaws. However, these aren’t fixed in DLCs, so my point still stands.
I remember the launch of mass effect 3 in 2012, when EA and Bioware removed all the prothean companion content (very relevant to the story) from the base game and sold it as 10€ day 1 DLC. They even boasted about “releasing a game for 80€” back then IIRC.