how good was the german player who missed the penalty kick
The German player who missed the decisive penalty was Jonathan Tah, and he was generally having a strong tournament and is widely regarded as a high-level defender rather than an error-prone one.
How good he is
Tah is a top-tier center back for Germany, so one missed penalty does not say much about his overall quality. Reports around the match framed the miss as a dramatic moment in a team shock rather than a sign that he is a poor player.
What the context says
Germany lost the shootout 4-3 after a 1-1 draw with Paraguay, and Tah’s miss came in the final round before Paraguay scored the winner. Coverage also noted that Germany had a historic shootout record before this result, which is why the miss drew so much attention.
In plain terms
He was not “bad”; he was a good international defender who happened to miss in a high-pressure moment. In football, that kind of miss is memorable, but it does not define a player’s overall level.
TL;DR: Jonathan Tah is a strong Germany defender, and the missed penalty was a pressure moment, not proof that he’s an inferior player.