> that I'd like to claim wasn't an issue when I was making them circa 2015-2017,

Well, I wouldn't say that the standards for (software) security were anywhere near as high as they are now. It makes sense that our requirements for things change.

> It's very, very, very, hard to believe there's 0 way for Apple to ensure an encrypted connection.

Sure there are ways, but without regulation I struggle to see why should/would Apple ever bother. Nor do I think that a forced way would be held to the same standards as the rest.

> Put another way, avoiding the global observations: If it's impossible, why allow watches to be paired at all?

Because they can't do much, if anything at all?