That's fine when you have someone willing to play a different role, but more often than not they just stay on the same role and now you have 3 DPS. Or they switch but they are diamond support and plat tank, so they are going to soft throw now on tank.
Communication breakdown will still totally happen, but it can't affect the roles people are playing anymore with 2-2-2. At the very least, the toxic person has to play the role they chose, and if they think they can do a better job on ___ then next game they can queue for that. (To note though with separate SR for each role you should at least get a competent member of that role who chose to be there).
I'm a firm believer that role lock was created because of social aspects and not as much gameplay (although in my opinion 3-3 is the most boring thing.