The interesting thing about 3-5-2 is that it was used for 15 matches, the first three (2 draws and 1 loss) before the switch to the diamond (that everyone wanted) and then it was used again after the diamond's problems for 11 matches (7 wins, 3 draws and 1 loss) before the switch again to the diamond.
The manager probably concluded the poor results in the first three matches had more to do with playing Blackett, Lingard, Fletcher, Hernandez, Cleverley etc. than the formation, in the second run of 3-5-2 matches he stuck with it because it produced the results and then dropped it when it didn't, it's not like he doesn't know what he's doing, he just isn't knee jerk in his reactions.
As you also mention after the Chelsea loss we stopped playing and in the first 10 matches we had 13 points, if we exclude those games we are left with a middle 23 match period, if we took the points per game ratio from those 23 matches and applied it to 38 games then we would have 86 points. I can't help but be optimistic looking at that.