Sepp,
While what you say about the status of AMCs is technically correct, the reality is somewhat different. The operator is free to have additional criteria in addition to the A, B, C as defined, but in order to do anything instead of that requires a formal approval of an Alternative Means of Compliance (ALTMoC). This is a process that involves lots of effort, time and money so is not practical for anyone but the largest operator. And even they complain about the waste of resources.
So in practice most operators of corporate aircraft are best sticking to the letter of the AMC. Unfortunately this results in bizarre things like the operator's home base being categorised as B and so requiring special briefing! Don't you just love EASA...