I like it, it makes it more useful as a standard class, instead or just being a support for every class. With the new MP system also means you can "spam" Vestiges instead of being restricted to the really low number of cast of Forbidden Sun in 2.
The only problem is cast speed tied to DEX, and having to waste a ring slot for it (this is a problem for all magic classes though).
Explain how being more restricted with stats makes it more useful...?
The magic bar is a new thing and isn't just about pyro, so that's a different conversation.