Water FS doesn't rez.
DS is ATK based, very powerful, good for high end quests were you just don't get many turns before dying so use your sp asap. It's 191 sp, not 190.
Earth FS reduces dmg taken by everyone in the team by around or over 50%, it's a very useful skill.
The killer job skill is not stronger than DS I don't believe, but I haven't verified this personally, the only thing I haven't verified personally. The previous statements I know from fact, so you can count them as 100% truth.