Everything you just described is my experience too, minus the part about having a lot of interests already.

The thing that I was describing is that, for whatever reason, the things that I find interesting are niche enough to others that I won't find people who already know/care about the same things organically. That's not much of an issue if you have enough interests to balance that out, but I don't really have that.

To put it another way, I'm not filtering for people who already have most of my interests, I'm filtering for people who share any of my interests, but that's already filters most because I'm into few things with little popularity. So, "connected to [my] interests?" Yes. "Fully"? No.

That probably sounds really lonely, but I honestly don't mind that much. Like you've described, most of the friends I've had for a while I can talk about whatever with. What I'm describing is mostly a mild inconvenience when meeting new people.