Marvin's argument doesn't really have any logic behind it. We're going to have 4 wide players, Sterling, Nolito, Navas and Sané. Same thing he had at Bayern with Costa, Coman, Ribery and Robben.
And because Sterling and Sané are very versatile players, he'll constantly rotate them and everyone will play 40 games a season and stay happy.
Then when Navas' contract expires next summer, he'll be replaced by Roberts on his return from Celtic. And if all goes according to plan, Nolito will be replaced after that.
So by the end of Pep's first 3 years, we'll likely have Sterling (24), Sané (23), Roberts (22) in the squad and hopefully Brahim or Sancho (19) coming through as well.