Again you express opinions. Reading data, Kerber never reached a GS final before winning AO. The most she progressed in a GS was a SF, same as Pironkova did. She hasn't consistently entered the second week of GSs like the majority of top WTA players. So it seems that her success with grand slams is similar to that of Pironkova before the AO title, not equal, but similar.
Try to read your original posts again and the adjectives you used. However, I do not know you in person to understand whether your attempt was to insult players and me as a user or to just express an opinion. If that was the case, then I apologize. The point of communication is to express your view in a respectful manner to others.
P.S. Using caps in forums is considered shouting. Shouting and usage of strong adjectives do not make your original point more valid.