So you try to use all of the characters instead of just sticking to three?I try to use all of my characters so that they all progress. This is how I work my parties.
3 party: Healer, black mage, physical character
4 party: Healer, black mage, physical character, jack of all trades character.
When all else fails, I must have at least a healer in my party. Always. Always always always. I HATE using items in a fight. I don't know why, it just bugs me. I don't mind using them outside of a fight, but I will not use them in a fight unless absolutely necessary. That means a healer at all times when I can.
I have a swap out system in place in every game I play to make sure all of my characters develop and get points.
For example:
Party: Character A, Character B, Character C.
Character A levels up to desired level (for example: 40)
Character A gets swapped out by Character D who has similar abilities. So if Character A was a healer, Character D is also a healer and will replace Character A
Character B levels up to 40 (is a black mage)
will be replaced by Character E (who is a black made, or maybe a red mage, or another job class that has offensive magical abilities)
and so on. Once Character D reaches the next desired level (50) they will be replaced by Character A, or maybe a third character, depending on the number of playable characters.
And yes, the games where they don't have those clear defined roles, you can bet I customize them so that they do.