It used to be more even to all rogue borderlands, but players whined about this (Fissoa almost dying and D'Hara being hit from both east and west), so Anaris made changes to have the monsters spawn strongest in the largest rogue clump (the West). First folks whine to turn down the monsters for eastern realms. Now you whine for the opposite of eastern realms not having it easier. People are never happy.
Lordless regions do attract rogues preferably to other regions. And low estate coverage attracts rogue preferably to other regions too.
Sure, but fine tuning can make a world of difference. Making the large hordes spawn in the largest contiguous rogue region, as opposed to all rogue regions, solves the "this prevents any realm from ever really being able to war another" problem. But it only worsens the "the realms with the lowest density are also the least affected by the rogues meant to keep density in check" problem. Theoretically, with the current course, we could have those hollow depopulated realms keep on growing, and growing, and growing, until the hordes overwhelm all of the most populous realms. I don't think anyone thinks this would be a good thing.
On the other hand, Fissoa and Arnor both have more regions than nobles (while I'm sure it used to be as such for Luria, the Realm List seems to suggest Luria has a lot more nobles than I recall?). And Fissoa is surrounded by rogue regions to keep expanding to. If the swimming hordes continued to spawn as they do now, but prioritized regions without knights as target breeding grounds to aggregate to, then wouldn't we be 1) applying the solution to its root cause (ultra-expansionnist realms) and 2) doing so in a way that doesn't interfere with regular realms' ability to do the PvP they desire?
A formula to determine a region's attractiveness to horde migrations could factor in: lack of knights, lack of lord, density of host realm (compared to average), region population, and region population percentage. As such, a region with no knight, no lord, in a realm with very few nobles per region, a huge population and 100% of its potential population would be considerably more attractive than a region with a knight, a lord, in a realm with a high density ratio, and only 1 peasant. Every other region would fall in between these two extremes.
To be clear, I do not have issue with the rogues in the West as they are. D'Harans do, I guess, but as general of Westgard, I personally do not. What I like less is the relation between our challenges and the actions of others over which we have no power. In a way, it feels like Fissoa is waging war on us with a battery of Big Berthas, our options being limited to healing the wounded and hoping we can heal them faster than they get killed. The underlying issue here is geography, I've made this point many times, but I think it obvious to all that tweaking monster behavior is far more likely to be done than removing all of these rogue land masses to crunch all of the eastern realms closer together.
I can't comment on the impacts of the new swimming code because I have no idea how it works, I have not been able to witness its impacts yet (I don't think anyone has nor will for some time). Personally, I don't think it, in itself, does much to address my cited concerns, it mostly just helps D'Hara retake Port Raviel. Eidulb and Candiels seem to have held just fine, nobody's holding the Northern pass, and Westgard doesn't hold any chokepoint at all. I can't really see great benefits for this change except for D'Hara, but if the monsters cross randomly, it could just be a step back towards the old "everyone is too busy fending the rogues to tend to their PvP".