Doesn't this just show market is very efficient and trading is useless
It shows that there are weeks and types of markets where the earnings trade does better on average than other times.
Have you looked at ways to hedge the the non-earnings part of the earnings straddles against declining market volatility? Vix puts, short index straddles?The best takeaway is to avoid times of elevated market-wide volatility if you like going long earnings straddles.