I'm sorry but that is totally unfair to say it is wrong to dress 'frivolously' or 'ostentatiously'. Those women you mention might dress superbly but I bet they chafe against the restrictions upon them- they do not choose those understated colours of a totally free will. Good on her for sticking two fingers up at anodyne, sexist and restrictive dress codes. Shame more women (and men) don't have the guts to do it. And that red dress- she was at a gala night FFS. Not in court.
I watched Amal's newsnight interview and she was dressed beautifully in a Marni rose print blouse and pale pants.
And Issa and DVF are very mid range when it comes to off the peg 'designer' clothing. Giambattista Vialli- that dress was not off the peg. Neither was her Oscar and Alexander MCQueen and Stella. All custom fitted to her (the Stella louche and looseness is deliberate, not bad fitting).
By god If I had her income I'd have everything custom made. And I'd ride a unicorn to work.