PID works fine if you parametrise it right, which is what this paper does. Consider the variety of inverted pendulums etc. that are used as as examples to teach PID control.
> No, the bicycle is unstable. PID doesn't work well there.
This is just totally wrong. Stabilizing an unstable system is usually the first goal of controller design. Different systems do require different controllers, but pid is _very often_ perfectly adequate. It’s probably the most used controller structure in general.