I see your problem. You don't watch your surroundings, if it's not in your crossbars it's not there. You need to look behind, below, above etc and then you won't be killed from behind.
What exactly is "assault"? CTF is in the game a lot....
And 343 did make the four new maps in Forge with Forgers. Don't try and say Bungie didn't reuse maps, they did, A LOT.
If you could run getting shot then you would escape everything and nobody would get much kills. And the radar is not broken, watch it or die, simple as.