Arsenal is one of the most successful clubs in England in this season's transfer window. They have strengthened and reinforced their squad and that is exactly what is needed to be able to win a trophy. Last season Arsenal competed very well against Manchester City, but it is due to their lack of squad depth that was the reason why they did not win any trophy. I think that is what they want to solve this season with this squad depth they have now, they can be able to compete for a title next season.
Arsenal is in fact the most successful team talking about this season's transfer window but the big question is: is that a guarantee that they will succeed when the league begins? Chelsea is one if not the most successful team during last season transfer window but we all know how it ended at the end of the season. What matters now is the players adaptation to the team style of play and the couch role too.
Not sure about Chelsea, because they only sold key players but at the same time, they didn't manage to bring in star players. Unlike Arsenal who managed to bring in great players in this transfer market, at least that is a big difference that I think Arsenal are still better at this moment. Moreover, Chelsea have a new coach and it seems too, the composition and or quality of the Chelsea squad next season is not so promising. Regarding Arsenal, although Arsenal have new players but the fact is they are used to playing in the Premier League. So yes, I believe Arsenal will be better than Chelsea for next season.