I think I got something!
Btw, just to clarify, things like Burn already covered a lot of that function. Somehow I assumed that people would get that off the technical details (i.e. plasma medium, Burn flame potency, etc), because I'm dense.
Take this for an example: the more fire damage you use at one time (treating dps as an actual live number; the derivative is as important as the damage itself), the more heat is produced in that moment, dissipating thereafter (with the dissipation reduced by adding more heat [both by slightly resetting timers and by the obvious fact that heat is added]. I could rack up heat so that each application of heat is improving the next in a steady barrage before heat is lost. I could have the full party blast one, then sustain the lingering damage of the cast with Bio--Aeroga with all that damage over time being dealt at high burn and without escaping the Bio.
Lengthier example:
When attacking 5 enemies with 5 casters [4 Conj, 1 Thaum] I could soak the middle one first, blast him with lightning for high heat enough to evaporate the water into steam, set him on fire while the heat's still up, Aeroga at different overlapping fields across mobs at high heat to distribute burning to the others, Dia the one in the middle, turning the overlapping fields into a larger, sustained whirlwind, use the basic fire spell into the AoE system periodically to conserve stamina, then Thundara the outside 4 with one cast on each, to bring them up to a heat enough to hit the plasma medium, swapping all heat to the middle through Thunder paired with the Dia, swapping to Bio during the cast, literally blowing up the first target for disintegrated armor damage and leaving blood.
From there, something like...
Cast Reflect on the system (designated by Bio), then blast Thunder from near the remaining 4 enemies to rebound the lightning damage + heat onto the other 4 enemies (who's heat will have only been at plasma medium for a split second or two). Finish them off, mostly doable by the damage over time over the next two seconds...
Or, taking advantage of the blood:
Target the other 4 from within the Bio, cast Water at them, extracting the full heat under water medium (heat will cause it to change mediums on next interaction [Bio delayed that]), getting heat through that way for increased fire damage and the damage over time until heat dissipates.
A lot of random shit thrown in there, including a returned stamina measurement (more like FFXIII alpha ATB than anything FFXIV's used), Reflect, and that Dia acts as a drawing center for nearby spells in addition to dealing damage over time based on Light and Bio holds a system in place while dealing damage over time based on lack of Light. But, that's just an example of gameplay.
Things like Meltdown would come from melting enemy armor, more literally. Plasma and very hot water, especially with solid mass in it (prior earth spells melted), would do well for that.
As for MP returns... I think that would come from something like elements within the caster's mind as well. Kind of like... Mindsets fulfilled by TP, that could be extracted for some purpose. I'll keep going when I get back, hopefully with this more clear to me. Sorry I only have a few minutes to write this. I'm sure it shows in the quality. : (
(Other members put off departure for a bit.)
**Yes, this is by now departing from the original idea, separate. I'm trying to create the place it fits in a larger picture that's still vague to me, and this came up when writing what I saw. This won't come up in any serious posts until I've at least mostly completed that "full picture".
My only point here was that at least a WoW-equivalent level of intricacy can be achieved from use of the smaller factors. Paired with angles, and enemy AI responses to derivative damage-dealing (the intensity over time), elements, and patterns of attack, it can be more than WoW-level.
If I also add in mechanics that have each member of the team trying to fulfill their own production of power as well, rather than being identical in both group (large-scale) and individual (small-scale) purpose, it can go way beyond that even. However, I wouldn't gun for that except coincidentally. I'm looking for aspects of the game to fit every part of it, such that each piece fits the whole as to be greater than the sum, etc, etc.