Arsenal have to be massive favourites for 4th place just due to their points total and games played, and that is before you factor in that they are now out of all of the cups and so have no distractions and the fewest games left to play.
On top of that they've been by far the most consistent team of the bunch, and in their last 20 games they've picked up 9 or 10 points in each of the 5 game blocks (3 x 10 and 1 x 9). So that feels like the team that they really are, and if you project that out to the end of the season they'd finish on 67- 68 points.
In order to match that points total, all of their top 4 rivals would have to play at a level of better than 2 points per game, which is equivalent to 76 points over a full season, or basically what Chelsea have done to date. That doesn't seem likely for any of those teams.
Arsenal's biggest weakness has been their games against the top teams (losses to City x 2, Liverpool, and Chelsea), but they have faired well against those around them beating Spurs, West Ham, and Wolves, with Utd being their only loss. Injuries to key players could really hurt them as well, but that is the case for all of the teams.
But having said all of that, predicting who is going to finish 4th is a bit like predicting who will win a race between a bunch of your p*ssed up mates running down the high street, it's basically trying to guess which one will trip over their own feet the least.
