Your point about what he achieved over a decade isn't relevant any longer. Football has changed and moved on. That's the issue here. Anyone with their head screwed on will always praise the man and show him respect for what he achieved but the line of evolution from then until now means only his legacy remains intact at Arsenal, not his managerial skills in this present day.
What you seem to overlook everytime is this isn't just about one game or one season. What happened last weekend ties into years of similar issues, moments in the PL when we've needed to show up and have gone AWOL. These moments have nothing to do with money, they are typically associated with poor set-ups and naivety in the team dripping down from the manager. Compartmentalising each season make little sense when we have the same players and manager and still suffer from the same screw-ups. Those two games away last season probably highlighted more about the problems with our opponents than it did about our own game. When you place that stat of one PL win against top four teams, which is poor enough in itself, into a wider context of the top 8 for example, we won a grand total of 3 from 14. You can see really, that win away to City doesn't demonstrate very much when we can't even put away the teams immediately below us.
The optimism before the last game was something we haven't seen for a long time ahead of a season and that has been absolutely trampled on. Ask fans how they feel about Palace and you'll get an unconfident response, rather than a certainty we'll bounce right back. That alone says a lot. Because underneath all the hope is the nagging feeling that we've been here before and seen the outcome. Sticking to a mantra of 'end of the season' isn't logic but a safety blanket to cling to, refusing to accept a dour reality that this season bleeds into the last, that bleeds into the last, that bleeds into...