I kind of have to disagree on all unicorn magic being the same here (and since there don't seem to be different subcategories of unicorns, your argument suggests there shouldn't be different types of unicorn magic either). Would you really categorize all feats of magic cast by unicorns during the series as just 'unicorn magic'? As in, different spells have wildly different functions, and thus are not the same. Sure, they're all achieved by using unicorn magic, but its use makes the magic being cast a different type.
By way of example, lets compare some of the different types of magic seen in the show:
- Basic unicorn telekinesis, which basically consists of using magic to move stuff around.
- The time travel spell, the effect of which is rather self-evident.
- The different kinds of transmutation seen in the show (mustache growing spell, GGG carriage creation, Twi transforming into a book illustration).
There are many more examples, but can you truly handwave all of these clearly different types of magic as just "magic"? As in, how would unicorn magic even work if there aren't any guidelines (such as its categorization into types) to casting spells with it? And if the magic truly just happens magically, why does Twi treat it more or less like science? How is it taught to anyone, especially in prestigious schools?
And if unicorn magic (the only "active" magic seen in the series besides alicorn (and most likely changeling plus Tirek' and Discord's) magic), why would the magic of alicorns be any different in this regard?
Also this.
I suppose that in order to clarify my earlier post, I should point out that by "types" I was referring more to the types of effects one can achieve with magic. The magic being used as a power source is more or less the same, I guess. Sorry for the scatterbrained quality of the post, by the way.