Well, the most disappointing of them all is Arsenal, their story is like the story of going from grace to grass, Chelsea's bad performance is quit understandable if you ask me, as I believe we all know that they had and probably still have internal issues, for Liverpool, I can't say as I have really paid attention to most of their games, but for Arsenal, I can't really understand what went wrong with them, they were like going to win the title this season, but all of a sudden, the table turned against them real bad.
Like you said, I hope they go back to the drawing board and find a fix to their problems before next season begin.
It doesn't matter that Arsenal are runners up in the EPL because it is not yet time for Arsenal to become EPL champions. on the other hand, it seems that this is not Arsenal's fault because it looked very good in the middle of the season and was able to reach the top of the standings after being eliminated again by Man City, it all seems to have become Guardiola's strategy, who succumbed in several matches leading up to the Champions League semifinals and the remaining EPL matches. .
so when the semifinals were near and the remaining matches in the EPL were few, Guardiola managed all the Man City players to briefly improve their performance to be able to win the EPL title and be able to qualify for the UCL finals. so this was already planned by Guardiola.