I tried RoM for the first time in at least a year this week. Got a fairly lucky start as (random) mongols, used their archer unique to take out all four of my neighbours on my starting continent. While growing into it, I was having a nice time clearing barb cities on my own continent, but once I popped a city onto an island just off the coast to get a couple new resource types, I started getting invaded at a just often enough to be annoying rate. So I decided to hop over to see where they were coming from.
The next continent over, about a third the size of mine, contained seven barbarian cities, all at least size seven (largest was, iirc, size 11), and literally hundreds of light swordsmen, archers, and wardogs, standing around in stacks at least 12 deep.
Spent hundreds of turns trying to subdue this small continent, not so much because I wanted the land, but just as an act of self preservation. After my third major offensive ground down, I gave up and decided to let them keep it.
The other half of the map, where the other three surviving (the barbarians wiped out one of the four that started on the northern continent while I was engaged in my crusade, and are halfway to taking out another) civs are is a long snaky continent where the other civs are still struggling to expand because the barbarians outnumber them so badly, along with a few large islands, each with at least one large barbarian city.
So. What setting do I have to adjust to get these ravening hordes to actually become civs like they're supposed to. They'd be easier and more rewarding to fight if they had sane numbers of units that could actually get my units the levels they deserve for the amount of fighting they have to do.