I'm a 3D modeller, I've been working with 3D for over 20 years. I've YET to see a useful home-model that isn't just "look - I - printed - a - stock - model - ma!" tech demo.
That is quite a sad statement. It also shows that you don't know any tinkerers, engineers, and instead surround yourself with people who would better be placed with just going out and buying a toy for Christmas.
I'm not a professional 3D modeller, yet the only thing I've used 3D printers for, or seen 3D printers being used for is hobby projects, repair work, some neat hacks of existing equipment, and upgrades. I personally have used it to add an indexer to an old broken coffee grinder which previously worked by jamming a pencil in the side, I've created adaptors to allow various vacuum cleaner parts to connect with each other, I made a small angle router attachment for a Dremel, and use it to build cases for projects.
Your comment is like saying that you've only ever see people use hammers to assemble IKEA furniture, all that means is you don't know enough diverse people.