A single Earth Government, such as exists in the Halo world would not have the scientific competition to advance as quickly as we are now. Currently, all the governments in the world are competing with each other to get to the market first, just like companies compete for products and pricing. Uniting together would stifle some of the scientific advances, especially because things like active camouflage, guns, and suits like the Mjolnir Armor are really only focused on for warfare. Look at things like the Spartan programs, which didn't come into development until the Insurrection. Humanity is best at making things when we're in a tight spot. The Shaw/Fukijawa warp drive that is used in the Halo games was likely invented once our solar system got too crowded. At that point, most of human science would focus on terraforming technology, and ways of adapting crops to new planets, rather than on massive warships and weapons. We like the idea that we are advancing technology at an exponential rate, it's what I've heard my whole life, but as a species we like to focus on something in particular. Currently, we are focused on computer tech, and integrating our physical world with the digital one. Even with the progress we've made in the last 50 years with computers, we are still quite a ways off from creating a dumb AI, and even further from a smart one, like Cortana or Black Box. Look at the computer technology present in the Halo games and novels. High Detail 3D holograms, Artifical Intelligence, HUD chips, and high-speed datapads. There isn't much more that we could accomplish with computers. Look at the medical tech. Biofoam, flash cloning and grown replacement limbs, thought controlled robotic artificial limbs. Cancer can be cleared up by a routine surgery in a few hours by this point. Look at the space tech. Ships capable of creating artificial gravity fields and supporting an oxygen-rich atmosphere, capable of travelling light years in a few days. Reliable cryosleep, impressive terraforming and orbital MAC cannons. The truth is, we have no idea when these things will be invented, or how quickly they will be implemented. It all depends on the people. The governmental and societal differences that occur in the Halo universe may veyr well have limited scientific discovery, and necessity drove humanity to invent solutions. Looking at things individually may be unimpressive, but looking at the bigger picture shows a huge leap in technology. The Covenant would still be a huge problem. Humanity is divided, the Insurrection is still going strong throughout the Human-Covenant War. Covenant tech is incredible, utilizing the inventions of the far technologically superior forerunners. The Covenant are able to create a device that can manipulate multiple magnetic fields and guide them to a target that can be tracked, cramming such tech into the size of a small gun. The power and precision needed would be incredible. Also, don't forget that they have the Huragok, who have a complete understanding of all things technological, and a memory of the incredible feats of the forerunners. The Covenant also have greater numbers, with Human planets only having a few hundred million residents on average, with a few big ones like Reach and Earth with a few billion. The Covenant consists of the Prophets, Elites, Brutes, Grunts, Hunters, Jackals, and Drones, each of which have incredible numbers in the Covenant Fleet and more still on their homeworlds and colonies that can be called in. Let's not forget their incredibly precise slip-space navigation, allowing formations to warp together, while human ships need to go alone, for fear of crashing into each other in the unpredictable slipspace. Energy shielding is also a huge bonus for them. Humanity doesn't get energy shielding until reverse engineering it for the Mjolnir armor. Point is, tech moves slower than you'd think, and the Covenant got a few thousand years head start, and were travelling space while we built pyramids.