I honestly would feel the opposite about getting a new acquaintance's contact information vs looking them up on Facebook and sending them a message. I've been going to a lot of weddings recently and phone/email exchange has been common, and I have yet to be asked "are we friends on Facebook? I'll put these pictures up there", which was a very common thing in years past.
Yours is an interesting perspective because I tend to assume that people on HN who say "just call your friends" are less social and don't have as many people they want to catch up with. Honestly events and groups are the real utility - there's where everything I care about happens on Facebook itself (aside from Messenger - which is good, but we would be doing the same thing elsewhere if it didn't exist).
Though the feed is still terrible - I keep my friends list relatively trimmed (~200 people) and it's still rubbish.
I don't need an algorithmic feed to tell me what my interests are and what my friends are doing because I know the first and there are other ways of doing the latter that don't involve giving up my privacy.
There's nothing wrong with calling friends up, but that takes a lot of work and a synchronous connection between two people. There are hundreds of people I want to know about or stay in touch with but don't have the time to call them all up individually.
Facebook makes being friends easier. That's a pretty solid value add. I would probably lose a lot of friends more easily if I didn't have Facebook.
You may not value that, but I find it much more valuable than the value I'd gain from making sure Facebook doesn't know enough about me to show me relevant ads.
Facebook supplies a directory of everything happening in my city, algorithmically curated against things Facebook thinks I will like and which my friends have said they're interested in attending. It lets me organise my own events, and communicate easily with attendees, who can see which of their friends are attending and make plans. It lets me make contact with people I briefly met in person but wouldn't have grabbed their phone number/wouldn't text them out of the blue yet (because who does that?).