There's a seam on the BB of my 1963 electro-forged Schwinn. They started with sheet metal and formed it into that shape. I'd say that it was a great idea when it was invented, but succumbed to higher precision and lighter weight techniques.

To make it cheaper, you could eliminate the weld and hope for the best. One of my kids bikes was that way. Fortunately it was outgrown before anything went wrong.