I don’t understand why you can’t Sprint backwards. It obviously shouldn’t be as fast as a Sprint, but more like an accelerated backpedal. I think this simple change would greatly reduce the double melee tactic, make the Sprint+Sword/Shotgun/etc tactic less overpowered (though still totally feasible), and actually make “Sprint” an armor ability. Nowadays, Sprint is thought of more as an absence of an Armor Ability. The only people who ever use Sprint in a playlist like Team Slayer are those who view AAs as a “crutch” of some sort, i.e. those who feel they don’t need one. I understand Bungie wanted to slow movement speed down so that Sprint would be useful, make grenades more powerful so that AL would be useful, etc.; I understand that Bungie wanted Armor Abilities to emphasize a particular style of play in an attempt to give players more variety in their gameplay. But I think they failed in that regard, because certain armor abilities are ridiculously overpowered (like AL, which we need not get into; like Camo, where you can stay cloaked for like 20 seconds if you stand still AND jam every enemy’s radar; like jetpack, which can instantly break map control, etc) while conversely, Sprint is underpowered. The very concept of unbalanced Armor Abilities violates the very principle of having balanced gameplay.
Hence, allowing those who choose the Sprint loadout to Sprint backwards (at a reasonable pace, enough to kill someone attempting a double melee with fairly well-aimed DMR shots, and enough to kill someone Sprinting towards you with 5 perfectly placed DMR shots; though these are merely my suggestions and suitable for debate as to just how fast one should be able to backpedal) will help balance gameplay, and perhaps encourage more players to use Sprint (and their weapons).