The game coding cannot require people to accept the scenario queue pop up. You cannot code people into playing the same way as other people.
I have been in games with six people and been the only healer. I have played in games where there were no DPS classes. That isn't the game designs fault. It is simple fact that not everyone that did queue up accepted that mission. I have also accepted the queue pop and then gotten disconnected after loading in. Then I have the coward debuff and cannot do SC fo rten minutes. That isn't my fault or the fault of the game itself. It is just bad luck.
Assuming that every issue you have with an MMO is because of game design is silly. People are a big factor in how an MMO is utilized.