Killing the other elves works pretty well actually. Just need to be picky on who to murder!
The vortex mechanics are truly a giant pain in the ass, with armies spawning in right next to settlements and often immediately attacking them (spawn and same turn move should never be a thing - impossible to react). Keep in mind you can delay hitting the ritual button and you still collect shards past the current goal (theoretically you could hit all the rituals one right after another if you waited) - I never hit the button until all cities have walls so you can delay a turn or two to get an army over.