and as I wrote, every time they perform an oratory skill roll, they gain experience
Yes, that's nice, but there are almost no Oratory skill rolls *except* for the rare Meritocracy option during Unrest - which has a catastrophic critical failure outcome off of skill check difficulties that are impossible to meet unless you *already have significantly-levelled Oratory*.
And who even has time for the Propaganda Assistant? It's completely random if you ever get the stratagem, if you have the Fate points, and, of course, if it's actually the governor in the zone having the event that has the Propaganda Assistant. Something as sharply limited as fate stratagems isn't a viable answer to a common problem. The Shadow Diplomat *would* be, if it actually covered Oratory too instead of just Diplomacy (which would even make it useful for the goddamn Foreign Council!)
Faction management ain't hard - shovel enough BP into your interior council and use Retirement cards to make leaders you don't want to go away - but getting leader skills is a complete crapshoot half the time due to the insane crit-fail penalties/lack of opportunity to train crucial skills for the leader role even over decades of active service and high capability.
(for reference - out of 40 leaders in my empire, 34 belong to my chosen faction, 5 to three others, and 1 is the bugged-out criminal syndicate capo who founded one of the non-favoured factions that I can't dismiss because he's not a leader under my control)
TLDR: Assassinate Leader is fantastic, but requires you to play Autocracy, the worst Politics-tier profile by a fair margin. Regular leader management isn't hard, just tedious (like a lot of things in SE). Many Leader skill gains and some profile gains are completely scuffed with events as they currently stand and lead to a self-reinforcing failure cycle.