I’m currently playing Age of Calamitous in singleplayer. I’d say the Devil Bear Cubs have been exaggerated - they’re tough, but as a late game enemy they’re not too bad (there’s worse things out there ). The Elarikan Plague is pretty deadly - certain creatures emit it when they die (plus some locations) - it stacks fast and kills like poison. But it doesn’t have to be a problem - there are certain special followers that are immune to the plague, and if you can get out of there fast enough even followers that aren’t immune will survive (it all depends how many stacks they get). Also the mod has recently added admin settings to reduce how tough AoC NPCs are and to reduce how much the Elarikan Plague can do.
That said, the mod is very grindy, and I’m not convinced I can see anyway (even at the endgame stage I’m at now) of finishing some of the end game content solo. A youtube channel I’ve found very useful is Yorkshirepuds Gaming - they might give you a clearer view of the mod (though it should be noted they tend to put themselves in dangerous situations at lower levels than they really should, so expect to see them die…).
After probably a couple of hundred hours in AoC so far, I still can’t entirely decide if I like it - there’s some stuff I really love, but the grind can get intense. The Singleplayer/RP add-on can reduce the grind a bit, but the biggest thing I would probably change is that I would have started by running Kerozards Paragon Levelling (and the special Smooth-Levelling add on for that mod, specifically designed for AoC) - base AoC levelling is much slower and grindier than the normal game, and I would have preferred the progression that Kerozards provides.
One mod I found quite fun that adds stuff, but doesn’t significantly change the base game is Emberlight - some extra weapons, a bit of decor, an overhaul of the farming system, some other bits and pieces. Another mod that adds a lot of content and changes is EEWA, but I haven’t tried it yet, so can’t say how hard it is.
I don’t know how much that helps - but maybe you can find something useful here?