For Devs de la Muerte, you can use an MK32 (grenade launcher), equip Drum Mag (One big clip but 30% ammo), and Scavenger (Kills return 10% ammo), then go onto the platform one below the top on either corner of the map and continuously shoot grenades into the center of the map. Drum Mag plus Scavenger seems to replenish all ammo on kill instead of 10%. When the enemies start wall-hacking, go into a bottom corner of the map, which forces the sniper not to be able to shoot you from below, and start shooting your grenades into the center of the map.
The end can still be very tough and chance is still involved. You need to get a big lead in the beginning, and you will probably die a handful or so of times when the enemies wall-hack. Also, if you spawn near the enemies or they spawn near you, you will mostly likely die. So there's an element of chance in that you spawn in a decent location far from the enemies. I did beat this mission using this strategy.
So decided to come back and try this. When I first tried this it was too laggy i couold not play at all. Now it is still a bit laggy but i can manage most of the time. Enjoyed this series glad to finish getting quests.