That's weird. Personally I don't find shotgun kills especially common. If you're in tight confined spaces, pull out your own, otherwise make sure you mark your entrances and exits so you can land on a headshot burst before they even get close to you. Shotguns are lethal up close, sure, but their range is absolute turd.
The stand out thing that kills me too often is Blade Dancer.
generally whenever i see the blade dancer show up in the kill feed i just run away from the Xs and the center point of the map as fast as I can. fuck trying to kill it and save teammates.
as for the shotgun/melee/shotgun shit.... many, i really don't know what to say other than there's really no reason to even be in that position when its so easily avoidable on most maps (fuck twilight gap). on top of that, every single jump and jump option puts you completely out of the shotgun's effective range
if you don't want to get sniped, stay out of the open areas and long sightlines - too easy
if you don't want to get shotgunned, stay off the ground when coming around corners and use your radar.
there's tons of shit you can't avoid in the game (warlock homing grenade, that guy in the match with the l33t throwing knife skills, titan defenders making objective maps a chore, etc) but the shotgun... man, that's really just something people need to be more aware of.
that venus map for example (shores of time), why are people even in that alley way near B? everything about that thing is a deathtrap yet people flood through just waiting to beaten into the dust by machine guns, shotguns, fusion rifles, grenades, and supers. the entire section is free kills to be had. but people are always in there. its their own damned fault.