There were mechanical computers before the 20th century that had more complexity (in terms of total information) and were more useful than quantum computers are.
Not true. Programmable looms and player pianos existed. They weren't Turing machines, but they were certainly more sophisticated than mere calculators. And of course there's the analytical engine, even if it was never built. These technologies were far more influential (both culturally and within the context of CS itself) and practical than QCs are. It's possible if electricity had taken a bit longer to develop that we would've seen honest-to-goodness mechanical Turing machines during the early 20th century. It's not like just didn't know how to design and build the machines, they were just very complex and expensive.
So if you want to make analogies between quantum and classical computers, QCs aren't even at the level of early 19th century technology. They're still trying to figure out what's even necessary to build devices of a practical size.
