Barca rely on him to do a lot of risky ' non goalkeeper ' duties. He's required to come out a long way to compensate for the high line and also use his feet to retain possession a lot more than other goalkeepers are required to.
Bit like Prime Neuer had to. And guess what Prime Neuer also made many similar mistakes like Joan's mistake today.
The only surprise is that it took him this long to make a mistake.
Nothing changes. Will be the best Barca goalkeeper ever and I hope he is the number 1 here for the next 10 years.