The Louvre, like all classical architecture, has a clear hierarchy in design language from base to roof, and it has only one mullion design. It's not all over the place like this one.
Good that they kept the mullions of the original design, it seemed like they were just going to put plain picture windows based on what looked like a test piece from a few pages back:
The mullions help to break up the squareness of the windows.
Design by spreadsheet. And people wonder why there's no "beautiful architecture" anymore. It was never the modernists to blame, but instead the cultural acceptance of cheapness and good-enoughism.