Arsenal basically broke even last summer, but that had alot to do with selling van persie. And before that cesc, and nasri. Their refusal to hold onto good players has finally caught up to them in terms of performances now. Persie carried the team on his own last year. This year it's showing. It's worked in the past, but it's getting too tight to maintain perfomance.
The Premier League summer transfers by Net Spend
Everton, tottenham, swansea all had a higher net income than arsenal in the last transfer summer season.
Yea, they probably overachieved in terms of league position compared to net spend for 3 or so years. But they didn't win anything and now they have a far weaker team.