If energy is energy, you should be able to convert one into the other, or at least use them for the same purposes. So, we take as a given that both sorcerers and druids can do all of the kinds of magic.
On the other hand, why would one prefer one or the other? Sure, they have some symmetry, they need a bias. In particular, we know that druids has access to a larger pool of energy (Nature mana). Plus you handicap sorcery in that it requires down time. That gives a remarkable advantage to druids. Why would one want to use sorcery?
I have some ideas:
Individual mana is limited, but it is readily available. On the other hand, Nature's mana is limitless, yet it flows much slower. This means that you can accumulate large quantities of Nature mana over time for a huge spell. However, if you need to cast on a pinch, you will be using Individual mana.
Using Individual mana hurts the caster, it might kill them. It would be foolish to use carelessly. Thus, anything done with good setup will probably use Nature mana unless there is reason to do otherwise.
The caster has much better control over Individual mana. Using Nature mana could result in worst precision. Meaning that anything that needs to be done carefully is probably done with Individual mana.
I want to note that we can workaround these limitations. On one hand we can have Nature mana stored for later use, and on the other we can have many magicians giving some of thier individual mana to be able to make a huge spell. Yet, executing these workarounds requires prep time and coordination. Thus, these are not the common case.
We can also argue that with training a magician could become better at controlling Nature mana, or increase their pool of Individual mana (or both). In fact, having these be two distinct paths of progression for an individual would mean that magicians would not be switching on a whim.
Which kind of spell would be done with Individual mana or Nature mana? all of them. The difference is not on the categories you have. Instead it is on their scope. However one will be more common than the other for each one.
Given that Enchantment is something done in preparation for later use, we can expect that most enchantment is done with Nature mana. (Heck, you say they use "cosmic power", I don't know what you mean by that, but I would bet it is not Individual mana).
On the other hand, complex enchantment might require finer control, meaning that magicians would have to use Individual mana to do it. Which also means that those are enchantments that are not done often.
I would also assume that there is improvised ad-hoc enchantment, something that a magician could do to get by in a dire situation where there are not many resources or time avaiblable. That could be done with Individual mana. Again, not a common occurence.
When we do a protection spell, does it last forever? I would expect protection spells to decay. That suggest that a strong protection spell is done with Nature mana (so you can put a lot on it, and perhaps keep adding).
Yet, on a pinch, the magician could draw some Individual mana for an ad-hoc protection spell. It comes at a trade off, of course, yet if it protected the user from a particulary nasty spell that took'em by surpose it might be worth it.
I suppose not all protection magic is negating casts and placing shields. In fact, I bet people who learn to make a seal learn to break it. However, bypassing the
security protection of a spell probably requires finer control than setting it up. In fact, magicians might not know before hand if we are going to have to do it, so no prep time. Oh look, they are preparing a nasty spell inside, we must break in fast! Making this a good candidate for Individual mana.
Transmogrifcation could be like surgery, you need to put the right ammount of mana in the right places. And to do that you need very fine control. Also, we are acting on a living and kicking being that will not wait for the Nature mana to accumulate. I think Transmogrifcation will often be done with Individual mana.
I do not know your setting, however, I can imagine that some special creatures could require much more mana than the average individual could deliver. Making the use of Transmogrifcation on them a large project. Perhaps some try with Nature mana, accumulated for the occasion.
In fact this could be a good situation to bring up the might-go-wrong trope.
Moving stuff around or doing chemestry with magic should not be expensive. There energy is there in the matter, the magician needs to channel it. I think Individual mana makes sense.
However, when it comes to converting an element to another, are we not talking about holding a nuclear reaction with magic? To convert lead to gold the magician will probably need a lot of energy. I know there is an argument for fine control here, yet, if it were to go boom fine control is buying you nothing. You want strong containment instead. Thus, I would suggest Nature mana for that.
Oh, about it going wrong? it would mean you don't get the substance you were expecting, or not as much quantity. It is about precision. So, no it will not summon a monster or open a black hole.
I can think of a few things to fall in here:
- Percieve what is far away
- Percieve mana
- Percieve the future
- Percieve the past (psychometry or trace scrying)
- Percieve luck? I do not know if that is a thing in your setting
- Percieve love? I do not know if that is a thing in your setting
- Percieve truth? I do not know if that is a thing in your setting
- Percieve... ern... microwaves?
Those are what? eight spell? Is that all from this school?
Future, past and far away are defying space-time. I'll put those on "needs a lot of mana" and say that people probably use Nature mana for anything significant. Which could mean that things could not be seen as clear or even predictions sometimes go wrong, makes sense to me.
Percieve mana has to be something usually done with Individual mana. Because I find it hard to believe that magicians learn to control Nature mana before percieving it.
As per other odd senses, I would say they are Individual mana too, following the same ideas as in Transmogrifcation above.
Of course Individual and Nature mana can be used for any case, yet some are uses are more common:
- Individual mana is often used for: complex enchantment, ad-hoc enchantment, ad-hoc protection, breaking protection, common transmogrifcation, trivial transmutation, mana perception, odd divination.
- Nature mana is often used for: common enchantment, common protection, special transmogrifcation, deep transmutation, spacetime divination.
There is wiggle room and I have mentioned things that I have no idea if they exist in your setting, also a few of these things could made less practical by the time to prepare the rituals. And as I was saying in the answer to your prior question, some of these categories could be underdeveloped, which is another way to nerf them. So, feel free to move around what I said. It is your world.