Many of the most famously incompetent emperors were in the early Empire, though the relative fame of the 1st-century Empire, and obscurity of the 3rd-century Empire, may play it’s part.
Many came from cities. Caligula largely grew up in military camps, which had similar water supply issues.
Adrian Goldsworthy suggests that in the early Empire, only senators could aspire to become Emperor, which led to incompetent Emperors but less opportunity for civil war and in the later Empire, any ambitious military commander could aspire to become Emperor, which led to more competent Emperors, but more civil wars, and the agentes in rebus, conspiracy-hunting, and the rest.
Hard to say, really. The roots of the Flavian dynasty were, at best, equestrian. (The word I get is that Vespasian’s grandfather was a centurion who married well and worked the family up the social scale - parvenus, in other words.) His younger son, Domitian, was the first emperor to actively cut the Senate out of governmental processes.
But there you have it - the end of the Julians led to the Year of the Four Emperors, and all four contestants, Galba, Otho, Vitellius and Vespasian himself, were the Empire’s top generals. I suppose it is correct to say that, from the start, the army was the way up in the Roman world, although the officer class was at least nominally equestrian during the Julian, Flavian and Nerva-Antonine dynasties.
I think it is fairly accurate to say that, from Marius on, de facto power resided in the personal loyalties of the legions to their generals, with all that implies about problems of succession.
I’d also heard the suggestion to keep in mind that our accounts of emperors are largely the creation of aristocracy-friendly historians. Which has better odds: that the bad ones were really that incompetent, and cruel, and narcissistic, and awful in just about every conceivable way at once – or that we are just reading inventions of their opponents?
I thought it was a reasonable point, but my opinion of those odds has shifted a lot over the last couple years. If Trump appointed a horse to some government position, my main surprise would be that he didn’t leave it empty.
I’m wondering if more left, or even just centrist, governments spend as much time threatening the opposition and the media. I remember stories about Brian and Mila Mulroney taking turns at screaming at CBC brass over the phone.
Then both the Bushes had their thing about “loyalty” – especially Bush Jr. and how he handled 9/11. Then Canada had Harpo and all the weird Imperial trappings he tried to add to his government, plus some of the weird insulting stuff he planned into royal visits. And then Trump being Trump, and then Doug Ford’s weird robo-texts which are phrased as loyalty questions.
That, and I always figured they have dreams of having a list of who to spare when they finally overthrow their own government and institute absolute power and their own version of Gilead.