@OneMoSalah
Playing and proving are 2 completely different things.
Lets start from the beginning. Borussia conceded 50 goals in 34 Bundesliga games in his first season there and 49 in second.
After that he came to Chelsea. First season was with Conte so 3atb.
Second season with Sarri... He started just 6 PL games. 3 clean sheets in those. Huddersfield, Brighton and Watford. Plus he played regularly in EL but again opponents that are a joke mostly.
For example against Liverpool it was 0:0 that season first half, Rudiger got injured and Chris replaced him and we lost 2:0. Not saying he is a fault ofc.
Season after with Frank again just 3 PL clean sheets with him against Brighton, Burnley and Watford again. In CL also nothing, he played 4 games we conceded 10 goals.
Last season he begun in starting 11. Brighton 1:3 win, 0:2 loss against Liverpool (thanks to him and that red), and two 3:3 draws against West Brom and Southampton.
After that he was benched and best period under Lampard begun. After start of the season he only played in 1:1 draw with Villa. He was good in Sevilla tho.
And now with Tuchel again 3atb.
I am sure others also remember stat that we conceded only one goal under Lampard in season and half with Zouma-Rudiger pairing. When you put Chris with either it is a disaster.
So when exactly did he proved himself in 4atb? In rare game against PL relegated team or against Hungarian or Greek side in EL?
When we play against top teams with 4atb and Chris is part of that and we have great defense like now with Tuchel while keeping regularly clean sheets then you can say that he proved himself.