I'm not sure how you don't understand this, this isn't an argument about 'blame' it's a matter of root cause for something happening. Auba was in red hot form when Arteta arrived, he won the Golden Boot in his first full season at the club, then almost got it again the season after and scored the four goals that won us the FA Cup some five months after Arteta took over
Also since Arteta took over the whole team has scored 20+ goals less than in the years before. Forget about Partey who's never been this bad in his whole career, Auba has scored 30+ goals in his last five seasons, now he's had a 15 goal season last year in Arteta's first and will probably add another one this year. If you can't see that's connected there's nothing left to say.