We know what Cardinal Müller said, it's his justification for saying it that is being questioned. He sees no contraposition with Familiaris Consortio but the Pope apparently does as he fully endorsed the Argentinian bishops' understanding of the Exhortation. Müller interprets AL in the same way as the Cardinals do, the Pope does not.
Again you do not comment on the fact that the CDF proposed several alterations to the text because it was unclear and liable to opposing interpretations and none of them were acted upon. If Müller thought that the document was clear, why would he propose these alterations?
Müller Is the Pope's doctrinal voice, he cannot speak on this issue against the Pope, he has to support him or else resign.