There has been no year on year regression over the last few years. I posted the points and final positions over the last 5 years in another thread, the few seasons prior to this one we've been pretty consistent, last year we got 75 points which is the same as the year prior to that. We finished 5th rather than 3rd as we did 2 years back because of Spurs and Liverpool's improvement, not because we regressed. Even then we won the FA Cup beating City in the semi-finals and Chelsea in the final.
This year has been a car crash in the league, mostly because of our away form. It will be our worst points total under Wenger and a massive decline from last year. Let's say we end up with about 60 points, that would be 15 points worse off than last year. Are you suggesting that we will regress by another 15 points and end up with around 45 next year? I don't believe that will happen.
Edit: I should add there is pretty much zero evidence for what happens next because under Wenger we haven't been this bad before. I am skeptical we'll fall lower because I reckon there's only so badly a group of players this good can fall, but there's no excuse for them being as poor as they have been this season so I guess time will tell.