You need to look at it from the opposite perspective
2 Years ago, we lacked talent in the team, and whilst Pjepje allowed for us to go 4-3-3, he also needed to help making the difference.
NOW however, situation is different. We have a team full of stars and awesome players. If Coman explodes, or if we want to give him chances, we'll need to go 4231.
Pepe doesnt need to make the difference in that formation, he simply needs to be the rightwing player we need to complete the formation.
I cannot stress how important players like him are, hardworking watercarriers who allow certain formations to work.
Busquets is a filthy untalented diving piece of asshole, but he was a "defensive midfielder" with the required passing to make their tiki taki work.