I think you don't get the difference between IM tab and Costume tab.
On the IM tab you wear the IM parts with your desired stats. If they look good for you you're fine. But in most cases players want to look differently because they don't like the look of the IM items they use to get the stats they want. Then you are able to change your look (and only your look) by using the costume tab.
By using the costume tab you can look the way you want while keeping the stats you want on your IM page. It has nothing to do with bragging because even Event costumes can be used on the costume tab.
I think you're missing the sense of the costume tab. And finally - it is not going to change how it's purposedly designed.