Mysticism was always ill defined but it DID at least include:
- Enchantments, the creation of, trapping of souls, and tapping and getting more out of enchantments
- Clairvoyant knowledge and perception
- Telekinetics
- Tampering with the flow of magicka
Now, if they'd gotten rid of most of that spell list I'd have understood why they did it. But in Skyrim they first merged mysticism with Alteration (Which speaks of altering the truths of reality, and does little to explain why it includes fields like clairvoyance and detect life) citing it to being a redundant field, and then created a completely new magical field - enchanting.. Which has perks relating to the creation of and the tapping and maintainence of enchantments... pretty much the description of mysticism in some of the in game books.
Is there some interpretation of the lore that justifies giving the mysticism spells to alteration, and giving the enchantment stuff to a new field by a new name ort have the devs simply derped? - because, far as I can see if they didn't marry mysticism to alteration and instead added the enchanting perks to mysticism they would've had a field that was both canonically more accurate AND would have justified retaining the school...
Also Alteration now seems to be the swiss army knife school. I mean it always HAD a really good selection - shield, feather etc - but now it has detect life and absorb spell too. An alteration expert covers just about every defensive and utility skill in the game