AppleWatch does have an IP rating. Apple rates it IPX7, which in practical terms means that you can go swimming with it. Apple doesn't boast about the water protection to avoid complexity. They're not going to explain that while it is water proof, you can shower with it, swim with it, but don't go snorkelling or diving with it. So they don't promote it at all.
Actually, Apple specifically warns against swimming in the Apple Watch User Guide:
As they point out, water resistance is not a permanent condition.
An actual watch is uncomfortable to sleep with. I've always taken off my watches to sleep, even before smart watches.
That's fine, but many of us have always worn wristwatches 24/7. Plus many people want sleep activity monitoring.
We're the ones who want the most comfortable watch case, and the longest lasting battery.
In my case, I solved the battery problem by simply swapping between two smartwatches. That way, one is always charging. Not everyone wants to do that, of course.