At least, because previously Arsenal managed to beat Manchester City, of course, this factor will make it predicted that Arsenal will also win against Chelsea. After all, we are all aware that Chelsea's situation and conditions have been devastated since last season, and have not improved until now.
Since the start of the season, everyone has been aware of how the two clubs are doing. This season, Arsenal has played really well, and they recently defeated Manchester City, which surprised me because I wasn't anticipating a victory from Arsenal. Chelsea's performance has been poor since last season, as we can see, but I can see improvement in Chelsea's performance. Chelsea is currently unpredictable, and they shouldn’t be underestimated. Chelsea will give it everything they've got to beat Arsenal or draw, and even if they don't succeed in winning, they might play draw. Despite the fact that Chelsea's last two opponents were not particularly powerful clubs, I can notice a significant improvement in their performance. Chelsea will be a difficult club for Arsenal to win.
I agree with you strongly, Chelsea is currently unpredictable so undermining how well they could perform against Arsenal would be a mistake because at this point I feel Chelsea is capable of a surprise, they have shown some level of slight improvement in their last two matches, although they had a not too strong opponent but their confidence and tactics showed improvement.
So it will be safer not to think arsenal would get an easy win over Chelsea because they won Manchester city recently, if wer are to properly analyze the game between Manchester city and Arsenal, you would agree with me they were lucky with the win the got over Manchester city, although they played well but later became defensive after their goal. I have always observed that weaker teams usually tends to show strength when ever they meet with bigger teams, such may be with the case between Arsenal and Chelsea nevertheless I keep an open mind to the possible outcomes but my favorite team is Arsenal.