I am sure this guy is way out of my stat range. Lost to him many times, even with people joining the attack. I barely deal 80 damage to him and he 1 shots me (I have war specials too).
You can take vicodin, use temps on them, get others to help (which I know you've done), rehab.... try everything before giving up and coming to staff for help.
According to rank triggers, both of you are in the same networth range, i.e. 200k to 2mil range.
In order to avoid him 1-shotting you, throw a smoke in your first fight and flash in subsequent fights.
Also, you can use a better melee weapon than whatever else you have equipped now.
Also, wait for the weekend when more ppl chain, wait for him to be left and time him coming out of the hospital so you need to deal less damage to defeat him.
When the target is assigned there is a rule - their defence should not be x14 higher than your strength. In this case you will be able to deal some damage. In this case this ratio is high, but acceptable (near x12), so the system worked as intended. However such situations may occur - when your or your opponent have unbalanced stats. You need to find some way to deal with them (group attacks, higher level players dealing damage first, boosters, etc) or just skip the mission if you think that it will not be worth the effort.