Then why isn't the Hydra better? It's the same kit.
Because it's the only non flier skyfire in the codex. And it's still damn effective for its points. Losing its jink ignore was pretty necessary to keep its points down, and the open top bit is largely irrelevent. They're still extremely strong AA, unless you're just going to rely on your 6-9 divination psychers and weight of dice to bring down air now instead.