Gern geschehen und ganz ehrlich geamint! :-)
What you say is also very true: the person usually making the hiring decision is the person who usually will be your boss! They do not want to jeopardize their job, now, do they?? And what if you start pointing out how things have been done wrong for a very long time? What if you turn out to be better than them and you end up taking their spot?? Plus, just like you said, the more competent you are, the less "malleable" you are going to be: what if you start challenging their decisions and it becomes apparent that you are right and they are wrong?? How is that going to affect their authority?
When you go for a job interview you truly never know: it is like a lottery. Some hiring managers, being confident in their own abilities, won't feel threatened by your abilities and will appreciate you. Others won't, just like explained above. Once I participated in a panel interview: my boss needed to hire a replacement for somebody who had left. It was a pretty important position. We went through a lot of people. At a certain point I thought we finally had the right person, but, no, my boss, the one had to make the hiring decision, said no! Let's keep on looking! I asked her: why?? "This guy has the necessary education, the necessary skills, the necessary experience, is very well articulated, has very good interpersonal skills, he seems to be a very good fit for our organization and our "corporate culture", he even expects just about the exact amount of money we are willing to pay.... Why???" Her answer: "Well, you know, if we hire somebody who is qualified for the job and already knows how to do it, then, within a short period of time, they just won't be challenged...." We ended up hiring this guy who was NOT qualified for the job, and was NOT half as pleasant as a person... I honestly think my boss felt threatened and wanted somebody she could easily manipulate.
See? When you go for a job interview it is truly like playing the lottery: you never know. Therefore it is important NOT to take it personally and keep looking until you find somebody who likes YOU! I have been part of many panel interviews and have also been a hiring manager: I have been on both sides of the hiring process several times and in my personal experience you just have to relax, be yourself and not take it personally: sooner or later somebody will like you. If you have lots of skills and experience, maybe too much for the position available, but they like you they will say: "Perfect! We will create a position for them and utilize them in many areas!" But if they don't like you, or they feel threatened by you, they will say "No, sorry, overqualified... They would get bored or leave in no time flat as soon as something better comes their way". If you don't quite have all the necessary qualifications, skills, and experience but they like you they will say: "Perfect! They will be challenged and they will grow into the position". But if they do not like you they will say: "No... They just do not have what it takes for this job, let's keep looking".
Do you see what I mean? Good luck, keep at it and do NOT take it personally: it is NOT you! We have all been in the same situation at one point or another in our professional career! :-)