I'm not M/GM so I'm aware that my opinion may hold less weight but I honestly don't think the tempest is the right choice. A long ranged unit that kills massive (after research) is cute but here's my suggestions.
I'd like to see the carrier take on the role of the long range capital ship unit (this might mean adding NonY's suggestions, or perhaps just a range increase in general?)... regardless this leads to the question... what's the natural stepping stone to carriers?
I suggest a new air unit that attacks both ground and air without having to charge up first, a missile based attack perhaps? The phoenix is nice but only attacks air and the Void Ray is fantastic... once charged, but it takes time to charge up and unless it goes into a battle charged it's often too weak to be useful. A versatile air unit is what I think Protoss need.
As for the Oracle... I like the idea of a flying caster for Protoss but I don't like its implementation. I'll go into that in much more detail when I release a blog later on
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