Roberto adds qualities to the team that are in short supply, so I like to see him start at RB most of the time. The only quality that Semedo has over him is man to man defending in the right corner. This makes Semedo essential against some of the more potent teams - like Real Madrid. I like Semedo, but I like Roberto better, especially against the weaker sides.
What we should feel good about this season is that Valverde has so many valid choices in picking the spots in his starting lineup, where both alternatives are appealing.
4-3-3 is back, with Dembele up front on the left. I expect scoring will go up, we'll have to see how the formation succeeds on defense.