"How bout *inset big-name RPG developer here* make *final boss rush fights* with puzzle?
For example, to face each form of Sephiroth, you'll have to solve a puzzle to unlock his next 2 forms after suffering gruelling battles against him"
On topic, the E4 + Champion is considered the final challenge of the game. There's no chance to fully heal yourself(since elixirs are rare) and your out of battle healing is only lmited by the amount of items you brought, which may sometimes be not enough.
The only thing GF is merciful enough is to give you the ability to save between each rooms. Imagine if they made it like the Battle Frontier where you'll have to face all 5 trainers without the chance to heal.
Action speaks louder than words. But words, when used right, overwhelm any action - Me, 2006 Let's put a smile on that face - The Joker, 2008