Tello doesn't deserve anything. He's a youth player who's being used often enough when we need him. Senior players unless they are incredibly below par will always get the nod. It was the case with Alexis a while ago and Tello played over him. Now Alexis is back on ''form'' more or less so Tello is getting less play time.
In football, the age, market value, name should come always after the performance in the pitch. According to your view, Pep should not played Pedro over Zlatan and Henry in that season. However, he benched them since Pedro was performing better than them. Pedro was also a youth player in that days. According to you, he wasn't deserving anything. However, Pep thought the opposite and gave him the deserved minutes.
Team always comes the first. If a 17 year old contributes to team more than a 25 year old than let's play him. Think about Messi. He was only 17 when he was playing. It is not about age. It is about performance and Tello shows amazing development in the last matches. He was deserving to be on the field in PSG away after his performance against Celta. He was deserving to be at least in the match squad in PSG home leg.
You say that Tello doesn't deserve anything because he is a youth player. It is the philosophy of Real Madrid not Barcelona. In Barcelona, Pep send Ronaldinho for giving Messi the deserved role. In Barcelona, Pep send Henry and Ibra for giving Pedro the deserved role. In Barcelona, we send Deco for giving Iniesta the deserved role. Your thoughts are opposite with Barcelona's philosophy.