The UNSC's tech is outdated for being 500 years in the future. Extremely outdated.
Humans now are already developing warp drives, active camouflage, exoskeletons, hydrogen fuel cell cars, nuclear reactors with zero emission, and more! While we certainly aren't even close to creating a 3 mile long super-ship, we should be far beyond that in, I dare say, 300 years! Maybe even less! Even a Spartan by then would be unimpressive!
For 500 years into the future, I'd be willing to wager that the Covenant would be little more than a bug to us. A nuisance.
By then, I would assume humanity would have things like... I've actually got nothing. What we could do by then is unthinkable. Maybe we can make stars go supernovae?
[i]What do you think?[/i]
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Doesn't war tend to slow certain fields of science? There were probably plenty of wars that will take place between now and then. We may spend most of our research on weapons instead of the other technologies the UNSC had.