The game IS still a work in progress, no matter how much you dislike hearing that. Who knows, maybe diving will be added later on.

Don't kill stuff when it's in deeper water and you won't lose loot.

As for swimming, all you need to do is to approximate how far you can go while still being able to get back/reach solid ground.

There is exactly nothing game-breaking about the mechanics. You just need to be smarter about how you play.