It would be if stopped to think about it. What made the Luci so formidible? That's easy the Shields. Without the sheilds two wings of bombers and couple of Leviathans could wiped her.
Instead, a seemingly invulnerable warship forces the fledgling GTVA to desperately search for ways to destroy it. They luck out, and find records from the race the Shivans killed to become top dog. But, memories of the Lucifer, a Shielded warship, drove the GTVA to develop weapons powerful enough to penetrate the shields of the Lucifer.
I had another thought about the Shivans, what if they're a Cybernetic species, created by a so old so as to make the ancients seem recent, programmed to do one thing,"Defeat the Great Enemy, at any cost." Such a command would make the Shivans, if they are learning machines, to become nearly unstoppable.
This would also explain the seemingly limitless number of ships available. Just imagine if the GTVA had AI sophisticated enough to not only direct the construction of warships, but pilot them as well(no not the Training Drones), even if the GTVA was destroyed, the AIs , if they were insinuated into the infrastructure, could go on as long as they had resources.