Did you read the novels, or are you making this **** up? Reach was attacked because it was a major logistics and shipbuilding center.
There were never anything like 117 Spartans. At least 117 people entered the program, but by the end of it there were only something like 30 people. Everybody else washed out or suffered deablitating side-effects from the enhancement.
Also you may have noted it was one Covenant carrier's troop complement versus the entire UNSC Marine Corps, and while the Covenant have traditionally been victorious in space, they have rather more trouble with their feet on the ground.
*** SWM looking for fun-loving, stable, over-clocked Athlon. Turn-ons include hours of gaming, surfing the web, hitting IRC and hunting pedos with Cheese. Turn-offs include system crashes, overheating, low FPS, lag. Gateways need not respond. -Shrike