LunarMongoose
King
We played with normal difficulty settings next but I got next to no barbs then. Probably because there was also no large wilderness on that continent. It was boring in comparison. So I prefer your settings with maybe some tweak setting to prevent large wilderness parts to amplify the beeline quite that much.
Yep, that's standard vanilla barb spawning rules: they try to get up to the target total number worldwide each turn, and can spawn in any tiles that no players have active vision of to try and achieve that. MM actually has some of the normal spawn restrictions removed; in vanilla (and in other mods), they also can't spawn near other barb units (because barb vision itself counted as active sight), and there was something else too I removed, I forget atm.
Anyway, large wilderness has to do with the mapscript, and its placements of player starting locations. Because large jungles and deserts have lower desirability values (among many other complicated factors in the starting location code), players can frequently be placed in ways that aren't distributed evenly geographically, and this can create large wildernesses.
I'm willing to consider modifying the barb spawn rules, but I don't see any good alternative solutions. If active vision is supposed to block it, then you have to respect all players equally and say anyone's active vision blocks them from spawning. And if you do that, you're stuck with random levels of barbs each game depending on player placement (which is really, really complicated and takes dozens of different things into consideration, believe it or not, heh).
That random geographical level is then modified by the target density value in the difficulty settings, and by things like the Raging Barbs option, but those are just scale factors; 400% of 5% is still only 20%.

So like I said, I'm open to suggestions if you want to propose a way to manage large wilderness, and lack thereof, but I don't see how without eliminating the active vision restriction (which I think a lot of people would find unsettling in-game). You'd basically have to say they're allowed to spawn anywhere that's not within x tiles of a city, or something. That would even out the spawns globally, but it would also keep them coming, from land, for the whole game. (The idea in MM was that they switch over to naval warfare, and drop raiding parties for land assaults, later on heh.)
Edit - I suppose you could just count the barb units on each landmass and pick the lowest one on each successive spawn, rather than picking a landmass randomly (by picking a tile randomly, so the larger landmasses get picked more often). I'm not so sure this is a good idea though... variety in the player experience is a good thing (low barbs means freedom to put lots of tile improvements up early), and conceptually, large unexplored, uncivilized wilderness really should result in large barbarian hordes. Just saying.


- you are too much focused on detail instead of the big picture, and you put too much emphasis on the later ages, but few games last longer than to the industrial age.