It's cheesy, it's unrealistic, it's against the law (of physics).
I tried to play early missions without grenades or proximity but it's a nightmare.
I can make grenades weight a lot more, so they are thrown in a more realistic way, but it's not a good solution for rookies with 20 strength.
So I make a suggestion for the devs: can we have an option so that throwing underwater use only 1/3 (or some other numbers) of the soldier strength? This should not apply to aliens, because, they are aliens.
Or maybe this behaviours is already possible with the ruleset?