What do you think it'd take to "fix" Alcinus? Would a lot less unreliable do it? I think it's fun that he is unreliable to the point of going barb and joining other civs, but I don't think the churn needs to be nearly so high. Or, for that matter, that going barb be inevitable.
Do you think having them start with 1 pop 2 city would be an improvement? I think that could be fairly easily arraigned.
On the topic of Alcinus: Right now, all I ever do with him is teach him some spells the AI knows how to use and send him in the general direction of someone I dislike in the hopes that he'll do some damage when he goes barb. The chance of him going barb at any point really makes me hesitant to use him for anything important.
A couple ideas: He could be given Crazed instead of Mad, especially with the new mechanic for Crazed. I like the idea of him occasionally randomly running off to hit something, and probably getting himself killed in the process (which then sends him to another civ, leaving the theme of his madness).
Alternatively, he could have a promotion with a duration that degrades to Mad. Perhaps even with a (not readily available) way to extend the duration, such as killing a living unit. So that if you work for it you can keep him sane, for a while.
(I like Crazed better, actually. The more I think about it, the more it sounds like fun to have him randomly wander off to find something to kill, but otherwise be a perfectly reliable spellcaster.)
Also on the note of Alcinus: The Dagger is really not useful because of how impossible it is for a Martyr to survive to the needed level. My personal preference would be for the Emperor's Dagger to be straight up built rather than upgraded, but with a national limit of one.
Also on the note of Scion spellcasters: The whole necromancy thing is not very useful, in my opinion. Banefire, for example, is a horribly weak spell that requires you to risk the life of your caster to be able to cast it once. I haven't seen the Wraith Lord necromancy spell... but that's because I've never had the opportunity to be safely attacking with a Wraith Lord. Could be that it's entirely worth it. But Banefire, at the very least, seems very outclassed by pretty much every other combat spell.
On the starting cities thing: That would only be a method of slowing it down, since you could still just found a second city with your first Awakened. But that would probably help, yes. Any amount of slowing down the Scions' incredibly fast early game would help.
EDIT: And I would certainly support Korrina having Arcane.