Modern control theory (not counting RL, which is rarely, if ever, used on live controllers) is essentially two camps: PID with tuning and MPC (model predictive

Modern control theory (not counting RL, which is rarely, if ever, used on live controllers) is essentially two camps: PID with tuning and MPC (model predictive control). There is some optimal control theory not in either of these camps, but it’s not the norm. The latter is often studied under the umbrella of optimization theory (convex optimization mostly), but most aspects of it are well understood for most systems we care about (with some notable exceptions, of course). I wouldn’t quite say that “even control theory PhDs have trouble now” as there is plenty of work done on the field and many cases are quite useful (but they certainly have many topics to choose from for their theses!) :)