"Fiora's Heal is the boost of morale she gives her teammates"

I'm sorry Stashu, and anyone else going with this flimsy explanation, but this exactly why is doesn't fit. Fiora is not a team player. Her archetype, the arrogant duelist attempting to prove themselves as the very best like no on ever was, and her lore & character, which state that she wants absolute zero help whatsoever, because in order to restore the honor of her household, she went off by herself seeking to face off against the greatest swordsmen the world has to offer _alone _, to prove she's the best of the best, not relying anything or anyone but her own skill.

You don't want Fiora to be a selfish champion, but you forgot that Fiora is an incredibly selfish person. No one would complain that much is Fiora was a gloryhound, "I do everything alone" type champion. We would more or less expect Fiora to run up to the enemy nexus alone without a care in the world for her teammates, and if the enemy team sent one person out to stop her, they'd get annihilated, and she'll lament how she 'Longs for a worthy opponent' as she destroys yet another tower, and pushes closer to base. These are more or less implied by her VO, her Lore, and her Subtitle: "The Grand Duelist"

Her character is the in-game equivalent of "1v1 me scrub, see what happens." Deliver on that.

You know who could use a skill like that though? Someone with an equally notable disconnect from the lore in their kit. Someone known to inspire their allies when they're losing, who turns the tides of battle by showing up and being awesome, thus boosting their morale to fight despite their grave wounds. Someone who leads the charge after giving his allies a second wind. Someone who should've had this heal on their Ult since Day 1.