I still feel like thief is underrated compared to IV and VI, and it seems odd that they get lowered so drastically for V. I wouldn't really want to play it on its own, as when I steal, I then just switch to fight the rest of the way (like with Locke)
Let me first point out that Edge is a Ninja, not a Thief.
Thieves in FF5 are actually very useful:
- They benefit greatly from the Brawl ability (I do this all the time)
- A high Agility stat means they will act sooner in battle, so they are very likely to get their turn before the monsters
- Full Moon and Rising Sun are back row weapons, which is great defense
- Innate Caution means you will never be attacked from behind
- Steal with Thief Glove
- Always dash and see hidden passages
They have so many good points it only seems fair to give them weak attacks. If you want a powerful Thief you can use the Brawl ability (double damage) and Full Moon/Rising Sun from the back row.