No they are not. Most people can't explain off the top of their head how the derailleur works to move the chain from one cog to another, or how freewheeling allows the wheel to move without the pedals to move, or even how the cable allows brakes to be remotely activated from the handlebar. Most people can't even explain why it is possible for a bike to be stable while moving but can't stand on its own. It's counter-intuitive.

There's plenty of ingenuity in the design of a modern bike.

Most of what you're describing isn't necessary for a bike. A fixie bike doesn't have a derailleur or freewheeling. And you can slow down without breaks.

You can even remove the chain. A penny-farthing bike is a surprisingly simple device. It is surprising it wasn't invented earlier.

My guess would be that they weren't invented earlier because they are not that useful without good roads.

My uneducated and probably missing a piece understanding is it was the other way around: good roads were demanded by and built for the cyclists.

I wonder how serious the improvements in rubber (esp. vulcanisation in the 1830s) were for the practicality of bicycles.

Bicycles were invented before tires, they were called boneshakers for that reason.

The chain requires some pretty fine engineering. Arguably jewelry makers had it.

205 years to be precise: https://www.bricsys.com/en-eu/blog/the-first-bicycles

Rubber. It's a product of the Americas, before that, wheels sucked.

the steering geometry of a modern bike is not entirely obvious, most configurations are either unstable or unsteerable. Plus a bike is unusable if you don't know how to ride it, so even if you stumbled on a stable steering configuration you might give up on it before you learned to ride it.

When I was a kid I taught my neighbor kid to ride a bike by rolling him down a hill. He crashed eventually into a wall (tangentially, so no great damage to him or to a bike), but he did ride bicycle after that crash course, no problem.