Are Arsenal Challenging?

Every season in the English Premier league most people always back Arsenal to go all the way and win the league but every transfer window every Arsenal fan and also other fans get annoyed with the lack of business they do.
Arsenal usually start of the season well, they perform great; having Ozil performing assist after assist, getting Sanchez to bag himself and goal or two every game nearly (definitely the main threat in front of goal for them) and if Sanchez is unfortunately injured or isn't on top form then they have Giroud who may have criticism from people but he can score over 10 Goals a season and with the team they have he can make sure he does it.
With the lack of transfer business this transfer window it's hard to see them challenging for the title but they always do up till Christmas then they slowly decline from top spot to Arsenal's trusty position... fourth.