What could be cool is having one or two relic(s) that influence the randomness of the spells. I could see at least in two ways:
A relics could drop to 0% the chance of a healing / buff / debuff spell being chose among the five possible spells. Same could be done for offensive spells or we could even force the esper choice if proper relic is equiped. As an example if the fusing on an esper offer 2 offensive spells, 1 debuff spell, 1 healing spell and the esper call, the "defensive" relic could produce a 50%-50% odds between the debuff and healing spells.
In a similar way, instead of theoric 20% chance for each choice in a vanilla odds setup, a relic could increase the chance of stronger spells (defensive or offensive), as an example a 10%-10%-10%-30%-40% odds setup.
Also I don't see Fuse as losing control of the character, it's more an uncertain call each time and the strategy rely on the esper equipped mostly. It's a bit like attacking with the pearl lance while being blind: your shot can either miss, hit, hit and cast pearl or hit and do critical damage. You're in control the whole time, you're just not certain of which possibility will occur. Rage on the other hand is losing control, but I see Fuse as an ability that can be chosen each turn.
A relics could drop to 0% the chance of a healing / buff / debuff spell being chose among the five possible spells. Same could be done for offensive spells or we could even force the esper choice if proper relic is equiped. As an example if the fusing on an esper offer 2 offensive spells, 1 debuff spell, 1 healing spell and the esper call, the "defensive" relic could produce a 50%-50% odds between the debuff and healing spells.
In a similar way, instead of theoric 20% chance for each choice in a vanilla odds setup, a relic could increase the chance of stronger spells (defensive or offensive), as an example a 10%-10%-10%-30%-40% odds setup.
Also I don't see Fuse as losing control of the character, it's more an uncertain call each time and the strategy rely on the esper equipped mostly. It's a bit like attacking with the pearl lance while being blind: your shot can either miss, hit, hit and cast pearl or hit and do critical damage. You're in control the whole time, you're just not certain of which possibility will occur. Rage on the other hand is losing control, but I see Fuse as an ability that can be chosen each turn.