'By 2010 it was clear that it had failed and that we needed a new approach. At that point we saw the first real sign of fallibility.'
Keeping us in the top 4 for six of the years since 2010 is not 'failure'. Especially when you consider that this period included a runners up place, 3rd place finishes and a smattering of FA Cups. All from a club with significantly less resource than others.
Arsene will have my eternal respect for that. It's a pity that others don't share that sentiment.
If I was going to take issue with your original post it would be that you present 'project youth' as some wenger indulgence that he had 'earned' by being successful. This clearly ignores the context, which is crucial- we were under severe financial restraint thanks tothe Emirates and he was trying to find a way of building a new team without the funds to buy or retain one.
His failing has been in the last four years or so where he has had much more to spend but has completely failed to improve the side, in fact making it considerably worse.
To look at that middle period without referring to the financial side is incredibly harsh on wenger.