To your first point, there is no way to prove you wrong because you are right: cobs are typically much cheaper than briars. Your second point has less to do with the briars vs. cobs than it does with 1. what tobacco you are smoking, and 2. how quickly you are smoking it.
If I were to offer reasons why briar may be preferable--that is to say not better, but why one would choose a briar over a cob--then I would offer the following points:
1. Briars tend to be more durable.
2. Briars have a greater variety in bowl shapes and chamber proportions. This can go beyond the merely aesthetic.
3. Briars season better than a cob.
4. Briars have greater resale value.
5. This varies depending on how the pipe itself is drilled, but generally, in my experience at least, the draw on briars tends to be far less open than in most briars.
6. And you touched on this already, but due to their perceived disposability, it's not uncommon for a cob to be hastily made with substandard stems, etc.
That all being said, I enjoy cobs, especially for sweeter blends. And I find some of them aesthetically pleasing. My first pipe was a cob, and I still have it. It is beat up and ghosted with cherry tobacco, but if I'm feeling nostalgic and want to enjoy a gooper aromatic or some Pegasus, I reach for a cob. As others pointed out, it's a matter of preference. I recommend any serious smokers to try many different kinds of pipes. The amazing variety available is part of the fun of this vice.