Needless to say I don't agree with your brother, at the end of the day Wenger's achievements in the last 10 years only really mean something to fans who value a top 4 slot, for me it was fine for a few seasons but when I realised that all it was was a cash cow and that we never competed or had a hope of competing in the CL top 4 soon lost it's appeal.
Wenger has proven he makes the same mistakes time and time again and that regardless of the scenario he can no longer deliver on the big stage, to keep him onboard for reasons other that football is wrong, he should be judged like any other manager would be at any other club, on results and in the end these haven't been good enough.
As has been mentioned he would have been sacked at almost any top club by now for some of the debarcles, he should think himself very lucky he's had as long as he has and seemingly continues to have as long as he wants to carry on without really delivering on the pitch. After 10+ years of relative failure sentiment should no longer get in the way of what is the obvious decision, that he should be relieved of his duties after yet another disastrous end to our season.
He's had plenty of time to right the wrongs and frankly failed miserably for one reason or another, it now seems he lives in his own little world, where everything is rosy and we play the perfect football and where winning is basically a top 4 place.