Right now, in Live Overwatch, the entire team revolves around keeping tanks up and working, because all other rolls are in service of taking space to capture the objective. It’s a pretty unbalanced experience, and it causes a lot of teams that have great players to devolve into competent teams that can’t win, simply because they’re not playing great the RIGHT way.
I think the primary goal of this change is to change the importance of tanks in Overwatch’s design and balancing. Healers and DPS will be encouraged to interact more because now both DPS characters will be as important to take objectives as their 1 tank character. And this also shifts the role of DPS to be much more active in controlling space and not just killing things, which I think is the vision for Overwatch as a team game in the first place. The simplified role of DPS in current Overwatch, conversely, is to just exist competently enough, anywhere near the enemy, to allow tanks to push in.