There are some excellent ideas sprinkled around the forum about barbarians, but it sounds like there are significant limitations with the editor (especially around when the advanced barbarian unit appears).
Barbarians have come to the top of my list of things I want to meddle with. With all my tinkering of settings (including auto-settlers, more early game units and around 66% more Civs on the same landmass) I've had the unintended and undesirable (for me) consequence of my beloved raging barbarians being regularly smothered in their infancy. The AI simply produces so many hunting parties the barbarians do not stand a chance even though land is settled much more slowly (which I thought would massively enhance barbarian power). Having viewed various threads (aren't forums great), I think the main issue was my complete ignorance that the AI, on all difficulties, gets a 200% combat bonus against barbarians (compared to say just 25% bonus for humans on Emperor)
https://forums.civfanatics.com/threads/does-the-ai-get-a-barbarian-combat-bonus.650911/.
I shall keep more of the creative examples others have tried in my back pocket to revisit if I have no success. But for now I'm going to start off simple. I view the very early game (first half of ancient era) as us all being barbaric and trying to rise out of the primordial soup to establish a secure empire of sorts. I think of turn 1 as the Civs and barbarian camps on a level playing field, but the Civs have the leaders with the ambition and ability to emerge from the dark ages (rather than steal cattle or act as mercenaries). So I would quite happily have a game where barbarians snuff out one or two Civs from existence or at the very least, destroy a few cities so there is more fog of war and therefore greater creation of barbarian camps. I also want anyone colonising an 'unoccupied' landmass to quickly learn the landmass was occupied all along and face devilish locals on camps created after a settlement is build on the landmass.
Also, my focus for barbs is up to mid-medieval era only. I also think a good way to test is to go waaaaaaaay further than you think you should and then dial it back a bit. And finally, I don't want the AI to have a major advantage compared to the player when it comes to barbarians (although I do want the AI to have some advantage as they struggle with being smothered by barbarians, e.g. hiding settlers and workers in cities for far longer than is required).
Sooo, based on some extremely rough calculations based on the assessment that the AI gets a 200% combat bonus against barbarians I will:
1) give the human a minimum of 100% combat bonus against barbarians on all difficulty settings
2) massively level up the barbarian spawns to Legionary (standard), Crusaders (advanced).
I wanted something more powerful than a Crusader but if I have barbarians with guns appearing in the mid to late ancient era that would be beyond comical in terms of immersion. I can see myself having to create barbarian specific units with enhanced attack and defence stats to overcome the AI combat bonus.
I think this will be a very fun and possibly disasterous test game!