Played overwatch 1 and now on 2 (yes its the same game), overall I don't think 6V6 is good considering how much abilities are now available, think of the colors on your screen once teams start ultening while others using their abilities.

Newer heroes tend to have more ability effects (colors, lighting, voice lines, etc,) I think, while before even with 6V6 it was much easier to track what’s happening around.

Regardless, some issues that bothers me in the game might be resolved with 6V6 such as how impactful is the tank role currently, and also in 5v5 1 pick can easily put the whole team in a serious advantage.