> At what cost though?! And no, I am not talking about money. Any device (and any product really) is a set of tradeoffs.

My $200 Moto G3 in 2016 had a removable back cover (admittedly not battery). It was also waterproof (and had a headphone jack.)

The engineering of making things waterproof is in the realm of "A bit more annoying but easily doable if anyone's interested in doing it", not "Doable at the cost of everything else".