You forget ancient humans forerunners and precursors. The tech that these badboys have far out match anything starwars can throw at them. You also forget its the entire universe at all points in time. This means the flood control a huge amount of ships same with the covies. thier fleet size rekts when they were in thier prime. The fight would be a long one but halo would win due to the mass amount of ships the forerunners have and can build.