Even if you do pump phoenixes after opening Stargate... Can't a zerg overwhelm the phoenixes if they are putting all their econ into mutas? Yes you can micro them to death but also committing heavily to phoenixes could leave you open to roach/hydra tech switches?
But I'm guessing this is relying on keeping a zerg contained with the phoenixes and not allowing a 3rd base and cutting their drone count in order to hinder their ability to be able to support such a tech switch.
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