Use of Mach speeds in combat

Most of the serious fighters and a few of the bombers in use today have Mach speeds in the region of 2.5.To acheive these speeds though takes the use of afterburner in most if not all cases, except for the F22 with its supercruise, and thus the use of a lot of fuel.In combat though high maneuverability, heavy external combat loads and need for range is generally preferable to speed so why the need for supersonic speeds in anything except recon aircraft like the Blackbird?Shouldnt simplicity, maneuverability, engines capable of long range and good lifting ability plus good countermeasures and other factors be more important than speed? Answers and explanations on a card please!