Let me think for a minute about the OP builds and abilities in the game:
Hacking - can clear a building without ever firing a shot.
Tech Weapons - can kill enemies through walls (and the mob just stands there).
Power Weapons - one shot mobs and the mob standing next to them with the bounce.
Smart Weapons - smart sniper rifles are like Amazon delivering death free with Prime.
Crafting - makes legendary versions of all of the above.
Healing items are beyond plentiful, work near instantly, and can be carried in the hundreds.
It doesn't take a "highly skilled" player to break the game, just someone willing to use part of what the game gives them.
There really isn't a good solution to this - the game needs a serious rebalance, starting with the dumb as rocks AI and working from there. The fact that video exists of a player taking a '33333' build through what is supposed to be the most difficult mission in the game really says it all.