Optimal would be having enough players that whenever an unexpected meta pops up you can build a competitive team out of your roster.

You have to also remember that on OW2 launch there will be 5 new heroes that players will have to deal with and teams will have to work around/with. You need to have players who can learn those heroes as well as stay on top of the current meta. What if one of the heroes is as warping a brig was, what if the hero doesn’t really do much until later, what if genji becomes meta again? What about the “right before playoffs patch” that drastically shakes up the established meta.

Get as many flexible players as possible