I think your last sentence is everything I am highlighting with my criticism of Martinez.
The fact that he is not Maguire (or to a lesser extent Lindelof) means he can do no wrong in the eyes of United fans. Your post makes it clear that you're not judging him on performances, you've just decided that because he's not Maguire, you're going to back him to the hilt.
All I am asking for is objectivity. At times last season he was very good...but there were also games like City away and Anfield away were I feel that were he not riding this wave of goodwill from the fans, serious questions would have been asked.
For the record, I have already said several times above that I think he is our best CB, but I'm not convinced that Varane is the right partner. I feel Martinez needs a real powerhouse beside him. Someone with pace and strength like prime Ferdinand, Ramos or van Dijk.
The way we want to play this season is going to leave us exposed at times. I worry there's not enough pace between Casemiro, Martinez and Varane to plug the gaps.