Translocator, Subtle knife, Mjolnir: uniques are unique. They're not supposed to be always better. They are unique.
As mentioned, a weapon that isn't worth anything to use may as well be empty space. If it's linearly worse than everything, there's no point in it existing, except for joke value. Translocator might have joke value, but it could easily have joke value and strategic use at the same time, and if there's a joke in the other two, it goes over my head. (Perhaps Subtle Knife is too subtle for me.)
It's novel to see a bad weapon, once, but after that you just ignore it. Or pick it up and set it down again for the register on your uniques record.
Basically, it's one thing if it's not better than what you have. I'm not saying that Mjolnir and Subtle Knife should compete with even the Butcher's Cleaver, let alone Longinus(which, realistically, most maingame melee builds will use). Just that they should have something that makes them have a theoretical use.
Frag Shotgun: treat it another way: you have spare space and no shells to fill it with so you take this and 10mm ammo. So if suddenly you're out of shells, you still can fight.
Your primary weapon is probably going to do more damage than a Frag Shotgun is, though, thanks to the incredibly long 1.5s shot speed. Even a Combat Shotgun's pump only takes 0.2, so it takes 1.2 per shot and is more controllable. And that's a common weapon.
Also, the question of why you're heavily running shotguns enough to run out of ammo for them a lot, while still holding tons of 10mm in stock, does come to mind. Learning to manage and balance your ammo better would be much better than running a Frag Shotgun.
Survivalist: main problem of this trait is that in DoomRL you need to kill your enemies, not die longer. That's why when you meat 372 revenants somewhere in hell, most players choose build that allows them to kill things faster. Preferably even before enemies shoot.
That's more of a question of what's effective when, which is really more of a general system balance question than one of that skill in particular...which means that it's basically out of the scope of Survivalist. Retooling Survivalist probably shouldn't involve retooling the entire armor/resistance system.
I admit, tanking is sort of a weird topic in DoomRL, but I don't think it's totally useless. Just not as good as other builds.
The main difference is that a heavily mobility oriented build keeps you in control more often(generally more valuable), a heavy damage build ends combat faster(generally more valuable), and a heavy defensive build raises the amount of time you can survive when you're neither in control, nor can damage enemies fast enough to drop them.
Generally less valuable...but not worthless. Sometimes you just go down a stairs, hit a group of two Archviles and four Hell Barons, and your Phase Device lands you in a dangerous spot too. Or maybe the entire level is a mess floor and it's just very difficult to avoid some damage. That sort of time is where two/three layers of TaN can slow down a lot of the damage you take, meaning that you'll be less likely to run out of healing on the floor, and more likely to be able to take valuable powerups with you to start the next floor, which in turn means you're more in control for the next, floor, etc.
The point I'm making is that Survivalist adds very little to that kind of insurance effect. So it's basically not helping with what I see as the advantage of tank builds.