The Spartan program was dumb, though. This is a civilization capable of building superhuman AI into a chip the size of a micro-SD card, they honestly should have been building huge armies of robots 50x more combat effective than a regular marine. They don't need expensive microfusion reactors, they don't need shields, they just need big guns strapped to a robot body. I guarantee you that a computer can react faster than any human can, even one with enhanced reflexes. You know what would run as fast as a Spartan? The suit of fucking armor by itself, without a human inside. It's already doing all of the work for the Spartan anyway, now you can just strap extra batteries and thicker armor on instead of having a human. Oh, and instead of a stupid human shape, you can make it mostly square to be more efficient. In fact there is no reason for it to look anything like a human, or to even have legs most of the time. You can have some of them with legs in case you need to navigate that kind of terrain, but honestly most of the time it's not necessary.
In fact why am I even calling it an armor suit. It should just be an autonomous 4 wheeler with a fucking autocannon on top. Then you can have a smaller version with a beefy fucking HMG on top instead of an assault rifle that can go inside and ruin covenant infantry. The lore goes on about how damn expensive all of the Spartans, you could get thousands of these vehicles for the price of one spartan. Real wars can't be fought by a tiny number of supersoldiers, it's fictional nonsense. The Spartan program's efficacy is based solely on it being designed to be a 13 year old boy's power fantasy of being a demigod in superarmor.