To add to the debate:
AIs are not required to use point-defense systems. It is mentioned in the first cutscene of Halo and a few times in the books that the on-board computer could handle point-defense, though not as well as an AI could. This goes for the main weapons and missile systems as well. The Archer missiles have their firing solutions plotted by the weapons officer usually, and the same with the MAC guns. It just so happens that the books follow Cortana and Spartan-117 primarily, so we see her doing a lot of the work. I have no doubt that Cortana would be able to plot solutions faster and with better accuracy on every account, but due to limited funds and the fact that UNSC ships drop like flies, it would be prohibitively expensive to put top-of-the-line AIs on every
ship. I imagine that the standard computer system aboard every ship is indeed a simple AI, lacking creativity but having great multi-tasking processing.
And to address the use of Spartans and ODSTs, it was in fact envisioned in a very limited fashion. The HEV pods are not out of the question at all, but, as already stated, in a ship-to-ship battle Pelicans would be doing the troop transportation. Pods would be suicide in a space battle. And T-Packs, while a possibility, seem like a fantastic waste of manpower with all the point defense and the inclusion of fightercraft. Also, it would be harder to get a good model for people strapped to packs, let alone get the FS2 engine to make them fly in a believable way through space. Slow moving bees, anyone?
I like the ideas and discussion, guys.