I just got out of 3 games where I lost. Why? I locked in my support/dps champ, and my allies all picked similar champs, we had no tanks. This means that we lost because no one was able to stick themselves out there for us. If there was a bar with recommended team builds set up, that simply told you how many champion types you had where, that would be nice. So when we have 0 tanks, it has flashing warning signs in the tank bar, and if there are too many of one champ, have the bars turn progresivly red to show that you have too much of that type/too few.

People would still not care.

Try to tell people that you need AP/AD/Tank.
Even if you have 2-3 AD they will pick another AD.