I'm not sure that proves what you're trying to say. It just shows that the UEF military wasn't in a great place when the GTVA kicked down the node after 50 years of peace, isolation, and - as far as anyone knew - guaranteed safety.
The UEF's economic and technological prowess, never mind its social cohesion, could produce a formidable war effort under the right circumstances. You can't say they haven't 'invested in preparedness' when their infrastructure is so well-developed. It's not hard to start making things what go boom and not hard to train the people to use them - at least not when you've already got good industry and education in place.
I direct you to modern Europe, which would be hard-pressed to deploy 10,000 troops on short notice.
It
does take time. We're not talking about a situation where weapons systems are simple like they were in the Second World War and even that took effort. The US fleet that won the war in the Pacific was authorized with the Vinson Bill in 1938. It took
five years from ordering to commissioning of the first carrier hulls, in peacetime. Specifications for the aircraft that would fly from them were issued anywhere from two to four years before they were fielded. You
cannot extemporize a navy. You can extemporize an army, but even in doing that you cannot expect to defeat professional opponents in open combat.
The economic and industrial manner in which the Shivans would be defeated, if that's possible, is going to be based on the Soviet Union post-WW2, with a professional military force plus massive stocks of equipment and material awaiting rapid mobilization in time of trouble.
This is because in the face of a Shivan invasion, the most precious of commodities is time, measured in weeks and days. There are no natural barriers worthy of the name to retard Shivan progress. Only force of arms can do that, and the force the Shivans can bring to bear increases exponentionally the longer the conflict lasts. Unless you can match that exponential increase in weeks, there's no reason to believe you'll win. Even being extremely generous and saying the UEF can produce a formidible war effort in three years...that's going to be two years and eleven months too late when dealing with the Shivans. Unless the ships are there in service or in mothballs, the fightercraft and weapons lines running a constant low-rate or even full-rate production in anticipation, then none of it is going to make a meaningful contribution to a war against the Shivans.