I would say Arsenal played well in the last season from the start of the season until the last few weeks but in the end, it seems they didn't give enough potential to continue their good performance and that's why Arsenal failed to win the title. I think after spending money on this team and hiring better and more expensive players, they are now in the situation to have a better chance for the next season.
I don't know, there are many examples where money can't fix the fact that a team can't become champions. Arteta may not have picked the right time, when the team at the end of the season was not as full of energy as it was at the beginning of the season. Both money and new players won't be able to fix anything if the situation repeats itself, but I think that Arteta should draw conclusions.