Dukeship has to be the most difficult title to get, even worse now than before.
It used to be that duchies were tied to cities and strongholds, which meant a minimum of turnover as these could be lost upon capture or to enemy takeovers. This automatically created a dukeship opening. Then, many realms had elections for the regions, which meant an election for the duchy.
Now, not so much. Realms that expand and take a new city don't automatically have a new duchy. And while a realm could have, theoretically, more duchies than ever before, there are absolutely no incentives to do so. From the realm's point of view, the fewer the duchies, in almost every case, the better. As such, frequently, when a new city is taken over, no new duchy is created. Furthermore, when a city is lost, the dukeship is not lost, so if the realm retakes it, no new election nor appointment is available. Dukes are appointed once for life, and never held accountable. Can't be wounded into forcing an election, can't be protested out or rebelled against. You can't even work with enemies to accidently lose the region, or to starve the duke out of his position, as losing the city leaves his duke and he can appoint himself to any other region if he likes.