Quality and anatomy maybe, but she's wearing little more than long johns with an asymmetrical pattern and a ridiculous hat that doesn't match said outfit.
That pattern might work for a flag but it doesn't for clothing. Unless specifically done so for a political purposes there's no good reason to dress like that. Something like the union jack in comparison works better because of the symmetrical nature of the design along with the large areas of solid colors.
If you had to base an outfit around the American flag there's much better ways to do it. What Zun did with clownpiece was the most lazy possible way to create an outfit possible. If you took the naked figure of a character, placed a stock image of a flag on top of it, then deleted the area outside of the silhouette and cut off the area for the head and arms you'd have the same basic character design with maybe four minutes of work. It's not the American motifs that are the problem nearly as much as it's how they're implemented.
The best way to implement American motifs into an outfit would be to primary focus on the colors rather than the pattern. you can make really well designed outfits using just red white and blue. Just off the top of my head you can have something with white thigh highs, a red dress, and a blue coat. To take that a step further you can go with striped socks(on both legs) and maybe a jacket with the stars on it. There's many directions you can go in if you get creative, which in this case Zun did not care enough to.
Even Doremy Sweet's outfit design looks like something someone at least 'tried' with, even if they tried while clearly being drunk.