Assassins tanks are fine except for "Terminate" by "Operations Chief" which is a badly designed move rather than making assassins a badly designed tank.
SuckaFish's 8man progression tank is a Sin.. If he can have it his way he'd probably bring 2 Sin tanks.
I think I said this during nim dg progression in terms of pushing a bit more raid dps, but I think 1 Sin and 1 Jugg are best atm. I'd still rather run 2 assassins than 0 assassins.