I actually did have fun with just the sims 4 base game for several months before I bought my first sims 4 DLC. So I think it's totally playable that way. But, in general, for me a lot of the fun of the sims is having tons and tons of options for stories, settings, activities, and characters. I own most of the packs from Sims 4, and I use content from all of them in various types of contexts.
Sims 3, I got the base game bundled with the supernatural pack. So I never played it as base game alone. It was the supernatural pack that made me interested in the sims games in the first place.