That's fine. You can make a car that looks like a Mercedes and no one will bat an eyelid, if you really made it with your own hands.

If you look at a game, and make your own that looks similar(or even exactly the same) - again, no one will bat an eyelid. But if you pirate the CAD files used to make said Mercedes and produce it using that then yeah, you stole their work without paying for it. If you pirate the game someone made without paying for it, you are also a scum. Whoever made it is not entitled to compensation, but you are not entitled to use other people's products for free.