Interesting thread, Flartchy. I think enough evidence, especially PVRhye's pic of Christina Hendricks, has been presented to show that women's secondary sex characteristics (large bust, relatively defined waist, wide hips: basically, the hourglass figure) can be fairly well accentuated by what looks like a lounge coat. Note that women's coats are often cut with bust darts, which tightens the fabric around the bust and so accentuates it. Also, they're usually short in the back so that the buttocks aren't hidden by fabric.
Your argument-schema is helpful, so I'll steal it. I think the real structure of your argument is:
1) Garments designed to accentuate characteristics x, y, z will not look good on persons who lack x, y, z.
2) Lounge coats were designed to accentuate broad shoulders and narrow hips.
3) Most women lack broad shoulders and narrow hips.
3) Therefore, lounge coats won't look good on most women.
I think all the premises are true. And on its face, the conclusion follows from them. Trouble is, there seems to be an equivocation, which Sanguis's post points out. It's true that the genus of lounge coats were ORIGINALLY designed to accentuate broad shoulders and narrow hips. But that doesn't mean that any lounge coat you see was ACTUALLY designed to accentuate broad shoulders and narrow hips. Many women's lounge coats weren't actually designed to accentuate those. The argument slides from the notion of actual design in premise 1 to the notion of original design in premise 2: but it can't do that if the conclusion is to follow.
One thing this thread usefully reveals is that we badly need some terms to describe women's tailored clothing, since the silhouettes of women's lounge coats and men's lounge coats in fact differ. They deserve different labels. I don't know what those should be. I just looked at my copy of A. Mansfield & P. Cunnington, History of English Costume in the Twentieth Century, 1900-1950
(1973). It's considered an authority on women's costumes, and does a great job of distinguishing different silhouettes and cuts of coats for men. There are plenty of undercoats for women described, but not many labels for them, apart from what you'd expect: "bolero" and similar. But the bolero is to a lounge coat what a lounge coat is to a morning coat. What we really need are labels closer in specificity to those for the different silhouettes for men's lounge coats: sack cut, drape cut, Savile Row cut, 1960s European cut, updated American cut, etc.
You're right that this deserves more discussion than it's received.
There was an interesting thread on some of these questions a few years back. A woman member whose handle is "Rada" got some suits made up in men's style: no bust darts, covering the buttocks, as I recall. There was some good discussion by knowledgeable tailors of the difference between men's and women's suits.
Originally Posted by Flartchy
1) Suits have historically been designed to accentuate male characteristics*
2) Women, by and large, don't have these characteristics
3) Therefore, suits that accentuate these characteristics won't look good on average-shaped women.
* "For example, in men's dress, the male suit does not just accentuate male bodily features, but adds 'masculinity' to the body." From Joanne Entwistle's The fashioned body: fashion, dress, and modern social theory