That's the thing though, why is apple the only ones authorized to swap out your battery? That service isn't free, and they're massively overcharging you for it.
It's also not impossible to build a phone that is water resistant and has a swappable battery, but that's besides the point. Personally I'd rather have a swappable battery.
The soaking rain thing has happened to me with a not particularly water resistant phone and it was fine. The water ratings are more intended for direct splashes and full immersion.
My opinion is that this is a comfort we can do without, especially given the ecology and consumer rights implications (not that a phone with a user replaceable battery is necessarily porous to water, plenty of phones meet both criteria)