How? Strategically and geographically they are almost identical.
This may be true, I'm not going to bother trying to analyze it right now (I'm going to watch some Battlestar Galactica with my wife, instead
).
The south in FEI has always been where the action is and the north is where no can get in and attack.
But however true this might have been in the past (which I question right off the bat), there's absolutely no reason that it will remain so. The north of the FEI has four realms in it—sure, Arcaea is the strongest, but that doesn't mean it's invulnerable. The north of Dwilight has, at quick glance, room for at least five realms.
As for getting in, on Dwilight, yeah, it's a little harder for Luria to attack Morek than for them to attack Fissoa. But it's far from impossible for
anyone to attack Morek. Swordfell, for instance, is perfectly positioned to do so. And frankly, at the moment, I would say that the biggest danger for Morek is that of secession, given how hollowed-out it is.
On the FEI, there are just two realms south of Arcaea anyway, and neither of them would have any real problem attacking it. So I'm really not sure where your comparison is coming from.