Every singe class can tank. They just have to do it differently, and some might need more help from a medic than another but thats not the point. It is about the fact that the game tells you who is allowed to tank and who is not. There are so many different situations in which taking a hit or even going full out tanking is the right decision. Just one example being tank and/or medic dead, currently the system tells you to remake the game because winning by tanking with a non tank obviously shows that you are a bad player. I have won enough of those games to know it is completly viable to win without medic/tank, but the game penalises you for doing what your supposed to do, win the game, instead of giving up. And there are enough other situations in which you might not go full out tank but still get some hits for doing something that helps the team, and every single time you get penalised for actually being and showing that your are a better player. Yes you get hit less the better you are, simply because you know how to react to a given situation, but that does not make the opposite true, because you got hit more your are a worse player. Yet, due to on hit system the game will rate you worse.