@PhMgBr As I mentioned in the answer, the word whopping is an informal word. It is not broadly used. All right? Just because you can find some examples on the internet doesn't mean the indefinite article is absolutely necessary. How many times have you heard people say "whopping" in your life? Just because someone says he is a native speaker, he must be right? Is that your way of thinking? —
Rathony 12 mins ago