He hasn't been let go. He was told honestly what his future was so decided to move.
If his issue was the amount of game time he would get next season, then Arsenal need to realise that to win the Europa League and both Domestic Cups (their best chance to win silverware next season, as well as get back into the CL of course) alongside playing an entire Premier League season. They will have to play a grand total of 65 games next season.
Thus since you cannot play the same 2 CM/CAMs in every single game (especially Ozil), it means that the Arsenal are going to need to have a total of at least 4 CM/CAMs within their squad. Long story short this would mean that so long he is fit enough, he can play at least 33 games next season and perhaps more depending on injuries/absenses/form of Ramsey, Ozil and Mkhitaryan.
So with the loss of Wilshire, unless they do sign another CM/CAM who is better than Wilshire. They are going to have to gamble to in the forms of Ramsey, Ozil and Mkhitaryan (and maybe Xhaka) when it comes to the CM positions in the lineup.
Arsenal would be cnuts to block that
That was not what I was advocating, besides it would be impossible for them to do so anyway thanks to the Bosman ruling. What I was saying is that Arsenal should have offered a better deal (as well as the Captains Armband) to Wilshire to persude him to stay, especially when there are (as I have said earlier in this post) plenty of games which he can play him in.
Anyone think he could have done a job as a sub? Especially when Croatia started pressing the Eng midfield?
I certainly think he could have done.