3. How many times to people really use flamethrowers underwater?
Not often, but it's rememberable because water slows down all movement, meaning that the Flamer is even more OP then when it's in air, because the aliens cannot dodge away. It's a soupy, ugly death.
I suppose you could argue that we are not forced to go into the water, but flamerdudes often have nades, so that means a heavy (alien) has to supervise him till he comes out or goes away.