Alicornutopia

Aside from any Pokémon connotations, I think Legendary is one of the best suggestions so far. Epic also works but has D&D/Materia style connotations, and Mythical has nonexistence-connotations.

Then again, they imply that the extra-special people always become famous legends.

If they go around using their powers much, they're likely to get pretty famous. Like, everyone knows that all the portals in the world were made by the Door, all the floating castles were made by the Architect, and so on.

But the hypothetical Healer leaves no lasting impression, and could probably avoid getting famous.

Sure. But then the ones who don't get famous are, tautologically, the ones nobody has heard of, so it looks to people like they always get famous even though it's really only likely and not certain.

Specialest, with an E

Adorable, but no.

What's the technology level of this world?

Pre-computing, definitely, but they might have like telegrams or something.

Specials?

"Changer" is now "shaper" because I like the alliteration with "shifter".

Tentatively going with "magically talented" for shifter/shaper/conjuror and "Legendary Talent" for extra-extra.