I feel like trying to have a little fun, here. This is slightly inspired by an earlier thread to solve a problem using the worst solution possible. This one, however, I'd like to see if we can present a problem and then provide a solution that would require the least amount of change within the game to achieve. Let's avoid restructuring entire classes, changing party compositions for existing content, and greatly changing the mechanics of a fight(s). Let's instead present solutions that are equivalent to, say, flipping a switch. Hopefully my initial examples do this correctly.

Problem: Parry sucks.
Solution: You can now Parry magic.

Problem: Vitality is the main stat for Tanks but many Tanks are deliberately avoiding it.
Solution: Vitality determines Physical Damage for Tanks instead of Strength.

Problem: Grade IV Materia are too expensive.
Solution: Increase chance of converting all gear into Grade IV materia.

Problem: Monks lose Greased Lightning due to deliberate boss untargetability.
Solution: If no vulnerable targets are on the field, freeze the Greased Lightning timer.

Problem: Skill/Spell Speed increases resource consumption.
Solution: Reduce length of resource restoration tick based on current Skill/Spell Speed.