It sounds like you don't understand the true way to break the game.

HP is not important; Evade % is far more important. Here is how much of a difference it can make:

We'll take a late game encounter, against some of those enemies whose attacks behave like Blood Swords. I don't remember the name of it, but here is how the battle might go:

With low Evade%:
The battle starts with the enemies ambushing you. During the ambush, the enemies take off large portions of your HP. More HP doesn't help, because the Blood Sword effect is proportional to the target's max HP. Perhaps one of your characters is killed this round.
Finally, you get to enter commands for your characters. Afterwords, the round starts, and the enemies get to go first. Soon, you now have 3 dead characters.
Following round, you try to run (or, alternatively, try to revive everyone). The enemies act first, and kill off your last remaining character. Game over.

With high Evade%:
The battle starts with you ambushing the enemies. This gives you a chance to berserk your attackers in the surprise round. (Berserk is actually a really good spell in FF2, provided you only cast it on a single target.) Perhaps you kill an enemy this round.
The following round, you enter your commands. You then get to attack before the enemy. In doing so, you manage to kill all the remaining enemies and win without taking any damage.
Even if an enemy does manage to get an attack in, it won't hit as many times, and will therefore only take away a small portion of your HP (like 1/8 instead of 1/2).

Notice the difference? Evade can mean the difference between a game over and a flawless victory.