[Micah]

The only downside? Hardly.

The phoenix still can't expand very well on its own and will never be able to take on large enemy forces by itself, which a real SC pretender can do. It also has no slots, so if you take it for F/A diversity you don't get to have a forge discount with it.

Sure, the phoenix shines when you're down to just defending your capital, but that's generally not a place you want to be at. The primary asset of the phoenix is just the diplomatic leverage of being a royal PITA to kill, not because you're a real threat. I don't think that anyone has won a competitive (non-noob/mostly experienced players) game with one, which seems odd for something with "no downsides."