The problem is that SE should've made groups of 5 people and not 4.
Now it requires that 2 from the 4 people are either tank or healer while in not 1 game you get that.
I mean how many games have you played were 50% of population is either tank or healer?
If they add new classes I can't imagine it will be better cause those who like to tank do that now already so I don't believe they will with a new job think wow lets start tanking. same goes for the healingclasses.
If SE would allow 1 more dps in a party and give all instances mobs more hp so it is same difficulty i think the problem would be solved.