I suppose the expectations were so low partly because of Arsenal's poor performance the previous season, so on the surface you could say Arteta has done a good job on lowering expectations.
However, it runs a bit deeper than that. There was an understanding that an overhaul needed to take place over the next year or 2. That started off mainly with the goalkeeper and defence last summer. And will continue with the midfield and strikers this summer.
So although you would look for an improvement on the previous season to show that what you are doing is having some degree of success, it's difficult to demand that big improvement needed for top 4 with a clearly transitioning team. However, in saying that, considering the shit show of a start to last season and we got 61 points, I myself was looking for something around the 70 point mark that I though at the beginning of the season would have us in the conversation for top 4, now I think it would get you 4th place guaranteed.
Last season after 22 games we had 31 points, this season after 22 games we have 39, which is pretty close to the target I had set. So to get to the 68-70 point mark, we aren't needing an improvement in form, we just need to maintain what we have been doing over the past 12 months.