There often is a problem with jacketings being made into suits. The trousers often won't hold their shape well and will bag. That's why there is a difference between suitings and jacketings.
Do you have any example for that? I have seen some claims that fresco was not good for a trouser to hold a crease yet there are fresco trousers made that can hold crease. I am curious if you have any examples of fabric that are only good for jackets and not trousers.
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But for those sporty materials that work as both jackets and suits, there is a difference between a sporty material that can work as just a jacket and a business or dressy material that works better in the more formal garment that is a suit. It's why a tweed jacket that has straight flap pockets and pick-stitched edges is still recgonisable as a sports coat. And it's why a plain charcoal serge jacket looks like an orphan.
This is like jumping from one point to another point without direct line of reasoning and make your conclusion based on that. Let me explain:
First, you said this:
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there is a difference between a sporty material that can work as just a jacket and a business or dressy material that works better in the more formal garment that is a suit.
And yet there is no explanation about *that difference* between the materials of make it dressy or less, formal or less, and other characteristics to support your arguments. Yes, there are differences in materials, we know that. However, what difference? We need explanations and ideas so that we can understand what and why you say this.
Moving on, you have this:
... It's why a tweed jacket that has straight flap pockets and pick-stitched edges is still recgonisable as a sports coat.
Now, a tweed jacket is a sports coat, whether it has patch pockets or swelled edge or not. That is fine. However, that has nothing to do with what I was saying. I am saying that if a jacket has swelled edge, since this feature is typically found on a sports coat/blazer/odd jacket, this suggests that this jacket is a sports coat/blazer/odd jacket. That does not mean that a sports coat/blazer/odd jacket must have swelled edge, nor must they have patch pockets to be classified as a sports coat/blazer/odd jacket, whether they are made with a sporty or city suit materials.
If, by your definition, since tweed fabric is a sporty fabric, even though they do not have patch pockets nor swelled edge, a jacket made with tweed is a sports coat, whether you have a matching pair of trousers or not. Then, by the same token, a worsted plain weave wool is a typical suiting fabric that is reserved to be used for city suit. Now, how would you explain why a jacket, made with plain worsted plain wool - a suit fabric, that has swelled edges or patch pockets, or piping around lapels, is then called a blazer? a sporty jacket? The material is suiting material but the construction can make the jacket as a blazer, or even a sports coat with different bells and whistles attached to it.
The base material is suiting, but the end result is not a suit jacket. Can you confidently say that only the material defines whether a jacket is a sports coat or not?
Now this:
And it's why a plain charcoal serge jacket looks like an orphan.
Is the example shown here is a plain serge jacket? Are we talking about a plain grey jacket without swelled edge nor patch pocket here?
This statement is not wrong, mind you. But the application of using this statement here to support your argument is wrong here.
