It seems to me that the right back position in a team is fairly easy to find cover for. Nothing extraordinary is required from the player. You don't have to be tall, you don't have to be left-footed, you don't really need to have a nose for goal, and you don't have to be precious. You do need, of course, enthusiasm, speed and focus. But it is not a position where clubs make huge investments. It is understood that it can be filled easily. In fact, top players that started in that position, like Puyol and Sergio Ramos, 'ascended' into a central defensive role. This is a position considered to have more responsibility, where special experience and steadiness are befitting, with more drama taking place in that area of the pitch.
Filling a Dani Alves sized hole
And yet, the departure of Dani Alves caused some headaches around Barça. When there were signs the player was beginning to feel uncomfortable at the club, Douglas was signed, which didn't turn out well for Zubizarreta. He came in season 2014-15, in preparation to take over the baton from Alves (who then re-signed) and proved himself to be worth nothing, except that he prevented Barça from signing Marco Asensio as there were not enough funds for both operations at the time. He did nothing at Barça. He was loaned to Sporting, and now he has returned. After him came Aleix Vidal, who couldn't play for the first half a year due to Fifa sanctions placed on Barça after which he was quickly ostracised by manager Luis Enrique.
Expensive search as Alves continues to deliver
In the summer of 2016, Alves left. Aleix didn't initially count and Luis Enrique called on Sergi Roberto, a good midfielder who managed as well as he could, but when he was put under pressure it didn't go well. Luis Enrique began to look more favourably at Aleix again, but just as the player was riding a positive wave of form he took a serious knock from Theo Hernandez that left him out injured. Barça pursued Arsenal's Bellerín, but have ended up with Semedo, originally an attacking player, converted to a full-back by Helder Cristovao, youth coach at Benfica. He cost 30 million euros. All considered, they have spent 56 million euros in search of an Alves replacement, who after producing for Juve is now off to do it at PSG.