minor point for those thinking there are better systems, bikes have been around a while and there very few new ideas, it is all refinements of existing ideas. We use derailleurs because they work, chain drive because it is efficient, cables because they are cheap and reliable.
I really fail to understand how some people can have so much trouble getting a piece of cable to pull a mech left and right. Why were exposed cables developed, because they actually help shifting performance by reducing the flex and length change inherent in the cable outers. Look at how cable outers are made, Brakes are spiral wrapped for flexibility and gear cables are a bunch of wires running the length of the cable outer with a very slight spiral.
Derailleurs do have downsides, which is why Sachs, Sturney Archer and laterly Shimano have done work on hub gears. But they are heavy, they are less efficient, there is not a huge amount you can do to get round that. Tools for the job.