Thanks for the reply, @Trismagistos!
That's kinda lame that I need the EP itself just to disable sentiments/lifestyle. 😕 I'm not that worried about irrational emotions/sentiments among my Sims. My gripe is that I don't want sentiments in my game, period. My newly-married Sims getting Flirty/Very Flirty every time they're simply in the same room together is as annoying as making them take cold showers, and apparently the only way I can make the romantic/Enamored sentiment go away is if I separate the couple for a few days.
If any devs happen to read this: Why couldn't disabling sentiments be an option in the Base Game if you were gonna implement a feature best used with the Snowy Escape EP? Seems kinda corny, honestly. I didn't really want the Snowy Escape EP, but it seems like I don't have much choice if I wanna get rid of silly Lifestyles & Sentiments that I never asked for and didn't want. 🤨