I used to thing this way before I realized it's just an arbitrary hoop you make people jump through. To you, people understanding TCP might be what you claim is a basic foundation. However, it's just about as arbitrary as asking people to explain 802.11 RTS/CTS or clos switch fabrics, which are both equally as important to delivering day-to-day network traffic. Additionally, they both can come up as things you need to understand when trying to optimize jitter/latency in sensitive local network traffic applications.

Don't judge people based on which components of networks they happened to take an interest in and dive into.

Part of the "problem" is that networks (even networks that span the globe) are too reliable these days. If a developer is developing network services, all they see is an input stream and an output stream. And that's all that matters 99% of the time. But add 0.1% loss, and all hell breaks lose because people don't understand the implications and rules governing the underlying protocols.

I learned a lot about TCP (including delayed acks), the basics of 802.11, and the basics of switching fabrics in my undergrad networking class, so I wouldn't say it's totally unrealistic for someone to talk a little about those topics, depending on the role.

On the other extreme, I've seen people ask why is that IP address divided by 16? (10.0.0.0/16)

And then you have to explain to them that it's divided by 2^16...