I get frustrated using melia. Her arts really dont seem to have too much of an importance. And I can only use 3 of the summon arts per battle unless she loses all HP and gets revived, so thats kinda pointless.
I've barely switch away from the arts that I have set for each character. I think I've only switched out 4 or 5 in total because I don't see the use of most of the others. I also don't fully understand what aura is about, I think I have an idea, but I still find it pointless at that rate so I don't focus on those arts.
I guess I need some advice.
Until I find Fiora, I ofen used Melia because of her buff ability.
You are wrong about her "3 limited skill per battle".
Fiora Melia has a double effect skills.
Each skill works in two direction:
First time it provide buff to the party (AGI up, regen, power up, etc.)
Second time, you release the elemental power to do damage to enemies : Water, fire, electricity, ice, etc.
You can "store" up to 3 power before you are forced to release them if you want to store new skill.
Each time you store a power, a light ball appear around Melia's head.
Select Water (give regen) > select fire (give power up) > select earth (give agi up) : You are full for the buff, you need to release them
press the center circle to cast them in the reversed order:
press 1 time to release earth (cast poison) > press 2nd time to release fire (cast fire) >
You can press a third time to release your water attack (absorb HP) to enemies, or do two new buffs to the party.
store > release
store > store > store
release > release > release (empty, you need to store new power).
I hope it make sense to you
About my party, I used a lot Melia / Riki / someone else (either dunban, or shulk when monado required)
When I found Fiora, I used her instead as she's powerful, she has a skill to reduce enemy's power and absorb it (25% more ATK power), she also has a skill to double the auto attack speed.
I often switched the members to increase their affinity, but I used a lot Melia and Fiora as leader.
Like you did, I sticked to set abilities and almost never changed them, I found the ones I liked and match my way of playing the battles.
If you like, I can list the skill I used, or detail how I used them. but it might be different than the way you fight.
About the user's skills tree, the tree column you unlock has sometime the same skill as other user but with a lot less AP needed. (for example Equip heavy armor takes less AP if it's in an unlocked column)