Very good post but if you don't think that xenophobia plays a part in this then unfortunately you are being very naive! Many of the people who attacked Ozil could not give a damn about Erdogan or even name a few of his policies but used it as a chance to go at the 'Muslim-Turk' Ozil.I don't really get the Podolski example (who BTW actually has been described as German-Polish when it was relevant to the context), if anything people not having a problem with him acknowledging his Polish roots does prove that this isn't about blind nationalism?
It's not like everyone in Germany is a nationalistic xenophobe. The AFD polls at "just" 15%, but the criticism was much bigger than that and came from the whole political spectrum, because when you endorse someone who is seen as a despotic ruler with ambitions of becoming a dictator and who also happens to antagonise Germany on a regular basis it's simply a political issue that gets everyone involved. Trying to reduce this to xenophobia is simply a cheap attempt at deflection.
The biggest culprit is the DFB though, they had to either kick Özil out because his endorsement was fundamentally at odds with the sort of values the association identifies with or they had to say that they don't care about politics. Instead they tried to sweep this under the rug, perhaps hoping a good WC would make people forget about it. But when die Mannschaft failed in Russia the management suddenly found its morals and made Özil the scapegoat for the early exit.
How they dealt with this is an utter disgrace and I don't think Bierhoff and Grindel have the moral authority anymore to keep their jobs.