They moved Mannfred out and added Festus so its kind of even in that regard. Festus is much easier to kill due to the ability to snipe his Dark Hold at which point he's literally a joke (and Festus himself, while a powerful lord in your hands, is a big, fat, slow, low armor target that even basic archers will murder in seconds). IMO it would have been worse fighting a combined Mannfred + Vlad double team, especially with the "dead rise again" mechanic.
As far as the other threats go they are pretty tame and usually not a problem for a long time. Skrag being successful and invading the empire is pretty low proability. Usually I find that Heinrich Kemmler eventually breaks out of his hole and becomes threatening but it takes a long time. The Changeling is pretty much a nonfunctional faction for AI. I feel like Norse is less threatening than WH2, probably thanks to Kislev and the chaos factions up there.
IMO the factions that need changes are:
- Daemons of Chaos (literally just complete shit, this faction is the brainchild of the lowest IQ worker at CA and has nothing going for it, shit economy, shit unit access until you have basically won the game, shit lord that doesn't get all the normal skills you want, etc etc).
- Ku'Gath (awful economy, slow as hell to develop, units are the worst suited for campaign. Literally only Ku'Gath himself is good. Also starts next to some tough factions.).
- N'Kari (as faction on its own they are legitimately decent. But he's unarmored and large and he's got unarmored troops and cavalry while fighting high elves where 50% of enemy units are archers and the other 50% are Lothern Sea Guard, so both archers and spearmen. Probably the worst possible matchup you could start with and elves are gonna dogpile you. Either need to be insanely aggressive at wiping out everything or just run away. It's also at odds with his faction mechanic of trying to corrupt factions over time cause you don't have time).
Everything else is generally pretty OK. Obviously its a chaotic game and its possible a lot of factions that hate you get powerful but that's a risk of many start positions.
Another thing to note is on VH/VH, or Legendary/Legendary you are expected to cheese the game instead just playing normally. The game pretty much cease to be a normal Grand Strategy game but pretty much become an optimization puzzle. Some startpos is easier than the other of course (e.g. Karl is probably up uuup there in difficulty) but really the startpos are not really designed around Legendary difficulty.
The difficulty modifiers honestly aren't that bad. The number of factions that you need to cheese significantly with rather than play as the faction is intended is pretty small.