People in your thread.
[snip]Always possible I've missed something, and if so, please point me to it.
Correct is, magic is magic, there is no innate difference between blowing something to pieces and call a Golden Saint from Oblivion. Galerion invented the schools for easier learning and understanding.
The schools though are three pairs of polar opposites. Three axes that form a threedimensional coordinate system (Axis 1: Destruction-Restoration, Axis 2: Conjuration-Mysticism, Axis 3: Illusion-Alteration). Every spell has a place on it - it can have zero on axes it doesn't have anything to do with.
Most magic effects are pretty self explanatory - example given the summoning of a Golden Saint. Others are tricky, like Absorb. It's at the centerpoint of the Destruction-Restoration axis, but that is because it loads equally high on both poles. This can't be, that's surreal - and therefore it was once placed in Mysticism in Morrowind due to this strangeness.
Changes of spell effects between games
are not lore.
Gameplay is not lore - if it were, then Cyrodiil, center of the Empire, would officially have only a fifth of the populace of a small island part of Morrowind. I've never seen anyone argueing for putting Command back in Conjuration.
The schools are pretty stable since they've got official lore, with some strange exceptions that were likely due to errors (Command) or genuine problematic cases (Absorb).
Either way, the schools regardless of how you look at them, group together spells by what they do. Not by knowledge of what you can do, but what they actually do. You don't become a better healer by blowing people to pieces, nor do strengthening yourself has anything to do with weakening the other. This is the Destruction-Restoration axis. Moving Resist magic effects from Restoration to Destruction, and Weakness from Destruction to Restoration, is maybe nice to get a new gameplay together, but has nothing to do with lore.
As for light, Illusion is not only the school of mind tricks, but also perceptive tricks often as the result of changing energies. Alteration is the school of physical change. If you make the light go all around you, so you're not visible, then it is a perceptive trick - and therefore invisibility is in Illusion. The same applies to Chameleon, Light and some other things. In Lore Illusion is described as "
warping the imperceptible energies of light, sound, and mind ". See the first item on the list

? By using your logic to shove light into Alteration, you can also put Chameleon, Silence, and Invisibility into it. They all work like light

.